The SPT is a good exhaust. You can find it for about $700 these days. I found mine for $350, but that price has disappeared. I'd go with mangnaflow if I were you.
I'm XPT stage 2 as well. Are you running the E85? Big diff over gas?Get yourself a nice dp and catback with intake and get xpt stage 2, I am currently running it and i love it. My current setup consists of Invidia catless dp, Spt catback, Aem intake (due here wednesday, thanks redcharge) XPT Stage 2 map, Cobb Short Throw, Innovate WB, and a stripped out shift knob (stupid factory plastic threads!!) lol
from what i've read before all you need for stage 2 is a DP and a tune. I wouldnt waist the money and get an aftermarket intake id go with the drop in filter unless the intakes on the 08 are as bad as you guys say they are. downpipe wise i think id go with cobb. i have heard alot of good stuff about them. if money is an issue there is a brand on ebay called SR*S. for under 200 bucks you can get an aftermarket dp. i dont recall if it is catted or not but i think it has a high flow cat on it. ive heard good stuff about this brand. they also sell uppipes for $80 catless with a flex joint and a spot for your egt if your a moron, and a catback for $200. but i heard that the catback is pretty loud and some people regret buying it. fitment on these items claim to be perfect oem replacements and people have commented saying that it was as well. i myself plan on getting a uppipe and DP real soon due to the fact that i just got my taxes back $$... good luck.