4 bolt turbos usually flow more thru the housing,But depending on what you are trying to do if you are setup for a 3 bolt it may not be worth the extra work
What are the goals? There is going to be some difference across the board..... but not until you go maybe sub 10 seconds does it have the potential to be the "bottleneck" IMHO.
With that said...there are plenty of 9 sec cars with 3 bolt turbos...... so take that into consideration.
