Re: horsepower gain
Well, your horsepower gains are going to be based off the tune your running. A mild street tune on regular 87 octane will net fewer hp than say a wild tune on 91 octane, but the street tune is probably better for your car and its engine if it's a daily driver.
The 05+ respond to simple mods like exhaust, CIA, and a tune way better than the 94-04's. I wouldn't be surprised if you didn't gain 30-40+ hp from those mods. Keep in mind this is a guess...I don't actually own a 05+ car. The feel of more power will be even better if you have an auto. The shift points and firmness will improve greatly.
I believe C&L intakes require a tune, so keep that in mind.
Just remember to get a custom tune. Do not buy the standard off the shelf, pre-loaded tunes, they aren't any good. Justin at VMP Tuning does really good with v6's. I think American Muscle also does custom tunes, but I haven't heard anything about them.
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.