How much more quickly would your typical wrestler (someone who was half-decent wrestling in high school) progress up the belt ranks in BJJ when compared to someone who starts out with no grappling experience?
I believe a wrestler would progress a bit faster just cause they would have a better idea on how to position their whole bodyweight on their opponent where a complete newbie wouldn't.
I would say all of them will initially progress more quickly than someone with no grappling experience at all. At a certain point, though, they will take one of two paths: rely too heavily on their wrestling and get stuck in a rut of aggression over technique; OR they realize the flow of jiu-jitsu can compliment their wrestling base - and then they become MONSTERS. I've seen a lot of guys take both paths. I for one really wish I had wrestled in high school at the least. Having to learn wrestling when your body is already beaten up and getting old is a bitch. But hey, good times.
Depending on your local particular 'strain' of BJJ, previous martial art (combat sport) experience will count for a lot.
In these parts (Australia) Blue Belt is often awarded when a player is consistantly able to dominate other White Belts. Given that WBs are 'novices' and often without any MA experience you'd expect 'trained' opponents, once they've got the basic BJJ strategy & tactics sorted out, with their existing skills to draw from would dominate their peers.
Once you've moved to Blue Belt however, I suspect you'll find that the other training becomes less of a factor. I had 17 years of Judo training to draw from when I made the switch and once I got my BB I found the level of competition (specifically strategic play) made a difference.
It can be initially frustrating being lumped with the beginners when you join a BJJ club when you have got some MA background but don't judge your abilities vs. other WBs, rather look towards Purples+ and you'll more readily appreciate how long the road ahead actually is.
Joe Macfarlane is a prime example (HUMBLEFIGHTER). He wrestled his whole life and was ranked highly in the state of NY (a wrestling stronghold).
He transitioned to bjj and embraced it. He was whipping on blues(w/ the gi) at 5 months. Straight up choking them and just out positioning and out working them. He was ripping purples in the no gi. His only problem at his weight class was Chad Beatty, a definite bad ass and a brown from almeida.
3 Rules for Wrestler Turned BJJer:
1) Stop turning face down.
2) Don't EVER straighten your arms out.
3) Being in the guard is NOT ok. Learn to pass.
The sooner you internalize these three rules, and also keep in mind that BJJ is NOT just wrestling with subs, the sooner you will become a holy terror on the mat that can give the average blue (or sometimes purple) belt a hard time.