Did the AP on my 06 as well and didnt notice much. Did a third gear pull next to a buddie with an 02-03 running the stage 1 map and we stayed even. The only power i had on him was low end. I have the stock boost gauge and pretty much hold a little less then a bar in each gear. 4th and 5 i go a little over. I think a bar is somting around 13-14 psi.
So yeah all in all i didnt notice much. I sold the AP and got a Ecutek. Not much change. In fact i wish i kept the AP because i ended up getting a new VF-39 and Sti TMIC from a local forum and wouldnt half to pay for a retune.
My two cents would to go from stock to stage 3