Is he really the P4P goat? top 5? - boxing heads please chime in 
He's in the discussion. Top tier.
How you rank that top tier really comes down to personal opinion and bias. We could argue all day about the order, I feel.
He is top 25 probably. He still hasnt beaten anyone else considered an all time great. That makes it hard to rank him ahead of others.
He'd be in the lower half of the top 25.
People are blinded by his undefeated record, which actually means nothing in boxing. Greatness in boxing is defined by beating the best opponents decisively, when they are at their peak too, and in multiple weight divisions.
Mayweather has not done that, because he pussied out against Pacquiao when it would have been the logical fight of the decade. He also waited on ODH until he was shot and DeLaHoya still gave him one of his toughest fights despite being 5 yrs past his best.
In no order: DeLaHoya, Trinidad, Hopkins, Julio Cesar Chavez, Ricardo Lopez, Sugar Ray Leonard, Sugar Ray Robinson, Marvin Hagler, Roberto Duran, Ali, Marciano, Larry Holmes, Marco Antonio Barrera, Frazier, Joe Louis, Kostya Tzyu, RJJ, and Pacquiao would all be ahead of FM because of that principle.
What's his best win? Yeah, that's why he's not up there.
He is ahead of RJJ, Trinidad, Tszyu, Barrera, Pacquiao, DeLahoya and Fraizer. The others mentioned are top 20 all time greats.
Not as great as they were and he wont have their legacy, but lets face it the sport has evolved so much that Floyd undoubtedly outboxes everyone
The sport as a whole, has done the exact opposite and has regressed quite a bit. Skills that were commonly seen in past era's have been almost forgotten. Floyd is one of the last truely skilled old school fighters. Nonito Donaire was being hyped as future legend, and look what happened when he ran into a guy with an old school skillset like Rigandeux. He was embarrased. There are very few trainers left who know how to teach defense and ring generalship. They are lost arts that are buried with all of the past trainers.
Avoiding pac in his prime is a stain on his legacy. But there is no denying he is probably the most talented fighter of his generation. 
I hold these p4p tournaments in my head sometimes, and from a purely physical standpoint FMJ can hang with any of my fantasy fighters. But I can't get him to the imaginary ring.
He is the perfect storm athlete: genetics - enviroment - work ethic...but the gladiator gods want more.
I think his place at the table has been earned with his skills and record, but he's not a bloodthirsty man so how do we find his spot among the killers?
boxing wiz - He is ahead of RJJ, Trinidad, Tszyu, Barrera, Pacquiao, DeLahoya and Fraizer. The others mentioned are top 20 all time greats.
No way he's 'already' ahead of Tszyu, Pac, ODH or Barrera at the least.
They all cleaned out at least two divisions a piece; they ducked NOBODY.
Fringe Top 10. He is technically one of the 5 best boxers to ever live when it comes to skills, but his resume is pretty weaksauce compared to the other ATG's.
I dunno. I started watching boxing in the 80s, so it's really tough to place him among fighters that I've never seen. Among the last 30 years, he's among the top 5 with RJJ, Lennox, JCC and a few others. IF he had fought Manny it would have been much easier to assess him.
Perhaps deserves a mention in the top 25 or so.
What division did DeLahoya clean out? Maybe 130, where he fought one time to win a WBO belt. Oscar lost too many big fights(Trinidad, both Mosley fights, Hopkins, Mayweather and Manny) to say he is ahead of Floyd.
And who did Kostya Tszyu beat to be called an All Time great? Winning a title from Jake Rodriguez and losing it getting absolutely destroyed by Vince Phillips is far from legendary stuff. JCC was 50% by the time he fought Kostya. His biggest win by far was Zab Judah.
Barrera was and is an All Time great. I don't think he is at Floyd's level due to KO losses to Junior Jones and Pacquiao. But he is a definite Great.
Pacquiao is an All Time great for what he did at 130 and less against Morales, Barrera and Juan Manuel Marquez( any of the weights they fought.) Pacquiao's resume at 147 is made up of all guys coming into their fights with Manny as damaged goods, and many of Floyd's left overs. Manny fought DelaHoya, Hatton and Mosely all right after Floyd had beaten them. He had the 3rd fight with JMM after Floyd had embarassed him too. Cotto was beaten badly by Margarito, and Margarito came in after a long suspension and off a KO to Mosley. Manny is quite what people think he is/was.
Only one mention of Harry Greb in P4P??
99.99999% of the people who post here have never heard of Greb. Way too far back in time. Or Willie Pep, Benny Leonard, Jose Napoles, etc.
Imo he is the best technical boxer of all time. Ppl say he ducked pac, I think he wins that fight fairly easily. Everyone has always been the one to beat him and no one has.
There are many ahead of him though in terms of legacy and accomplishments.
I would put him somewhere in the top 15 goat.
boxing wiz - What division did DeLahoya clean out? Maybe 130, where he fought one time to win a WBO belt. Oscar lost too many big fights(Trinidad, both Mosley fights, Hopkins, Mayweather and Manny) to say he is ahead of Floyd.
And who did Kostya Tszyu beat to be called an All Time great? Winning a title from Jake Rodriguez and losing it getting absolutely destroyed by Vince Phillips is far from legendary stuff. JCC was 50% by the time he fought Kostya. His biggest win by far was Zab Judah.
Barrera was and is an All Time great. I don't think he is at Floyd's level due to KO losses to Junior Jones and Pacquiao. But he is a definite Great.
Pacquiao is an All Time great for what he did at 130 and less against Morales, Barrera and Juan Manuel Marquez( any of the weights they fought.) Pacquiao's resume at 147 is made up of all guys coming into their fights with Manny as damaged goods, and many of Floyd's left overs. Manny fought DelaHoya, Hatton and Mosely all right after Floyd had beaten them. He had the 3rd fight with JMM after Floyd had embarassed him too. Cotto was beaten badly by Margarito, and Margarito came in after a long suspension and off a KO to Mosley. Manny is quite what people think he is/was.
Manny's win over Hatton was much more impressive than Floyd's because Manny fought him at a weight class Hatton was actually experienced in. When Ricky fought Floyd at WW he had 1 fight there in which he looked poor against a bona fide journeyman in Luis Collazo.
Manny fought Hatton at 140 (where he won multiple world titles) and utterly destroyed him in less than half the time Floyd took to get him out of there at a weight class that Ricky had a very poor/nonexistent track record in.
Do I think Pac has the better overall resume though? Probably. It's very close but even with Pac's losses his wins over Barrera are so far above any of Floyd's victories and the fact that Pac won world titles in eight weight divisions compared to Floyd's five gives his record the edge in my opinion.
If he beats or ties Marciano's record I would put him in top 5