I don't know of many that would push open source over cobb to the general populace around here. Both of them have their place.
On topic, it seems to depend on which map fits your specific car better. If you are considering the Perrin maps, I would order the AP off of Perrin. Just because you got it from Perrin doesn't mean you can't download the Cobb maps and try them out.
Just do me a favor and after you flash any OTS map, learn to do some logging to verify everything is okay with it
Down pipe wise.. I wouldn't be concerned. If you are shooting for big numbers down the road, you'll probably replace it with 3" the full way. The air cools off pretty rapidly at that point, is hence more dense, and requires less diameter to freely flow. At your power, I wouldn't expect a difference. If you want to leave the option open, get a 3" and the 3" to stock adapter from grimspeed.