There is a difference between what a part will support and if you will gain power by changing it. A 2.5" exhaust will support 350hp, but that same car may make 400 with a 3" exhaust.

A good inake will gain power, however the stock one will do fine if you do not want to get one.

I myself have switched back to the stock intake mostly because I dont care for the load intake sound, but have lost noticeable hp in the mid and upper end