Probably about 25 HP give ot take. But what you will gain is alot more punch, better throttle response, and even with the performance tunes, better MPG. I am running Bama's "race" tune as a daily driver. I have a 5/m w/ 3.73's. Before I was averaging about 25 MPG on the interstate. Now I am averaging 27.3 on the interstate and about 17-18 in town. It will wake it up that is for sure.
Location: PA to KY ('07) to IL ('09) to MS ('10) to FL ('11)
+1 on roughly 20-25 RWHP (sometimes a bit more) gain with a tune-required CAI & a good custom tune. Just a stand-alone tune will yield about 15-20 RWHP gain on an '05-'09 4.6L; and about 1/2 that gain on the '10 since they're already running the shoddy FRPP tune.
The Bama tunes from AM are a pretty good set of tunes. I am not pitching a sale for AM at all, but if you buy a CAI / tuner combo from them, you get free tunes for life. You really will wonder how you ever got along with out them to tell you the truth. No it is not 100 bolt on HP, but it is money well spent and you WILL be able to tell the difference.