Exhausts...cat back vs. exhaust

[adrial]

It's decision time for me..
Option 1: 3" cat back, leave the rest stock for now. At a later date upgrade to 3" test pipe and downpipe. Does the 3" downpipe improve performance in a car running the stock k26/8?
Option 2: 3" test pipe, get the 3" cat back at a later date. However, if I want to upgrade to a 3" downpipe, I would have to sell the current test pipe and buy a 3" test pipe that works with the 3" downpipe.

A key point is whether or not a car running 15-17psi boost on the stock k26/8 would benefit from a 3" downpipe. If it does benefit...how much?

Also in question is whether the 3" test pipe will work with the stock exhaust without too many problems...aside from buying a 2.5" to 3" adapter.

thanks,
Adrial

All above mentioned goodies would be bought from http://www.speedforceracing.com ...gotta take advantage of that sale now