To hit 300WHP you will need SRi/CAI, FMIC/TMIC, TBE, Upgraded BPV, Plugs, Possible FP Upgrade, Tune. You can probably push over 300WHP without a tune and with a MBC with a Map Clamp, but the tune is better and suggested.
In that case...which tune?
SB - If you plan to go Big Turbo or run a 5v Source like Meth, then the SB is the one for you hands down. However, the SB will cost a LOT to get tuned. For a full Tune you will need the SB ($650), PNP Harness ($300), Full Throttle Flash ($500) Tuning (Hourly rate, probably 2 hours min) on a dyno then street tuning to fine tune the maps (More $).
AP - Plug it in, flash, unplug and you're done. Out of the box tune and the 103 Maps are out to download and they are really good IMO. No support for an external 5v source and no custom tune till after the new year. Which in Cobb Terms might be 6 months from now or more. The AP is a Flash and not a SB which lies to your ECU and is a much preferred method of tuning for safety reasons.
With the mods in my sig MINUS the DP (only had a test pipe) I put down 289WHP/296TQ. I'm sure with the DP I should be very close to 300WHP now.