I think a valid point that could (should) be added is that a stock auto trans 2010 with a head, cam and headers change easily puts down 430 to 450 at the tire on a mUstanf dyno with a conservative tune. No need to go to a 427. You even keep the DOD option. If you are will to get rid the DOD (which I hate) then you can get a bit more agressive with the cam (still super street friendly) and make 465hp and 440 ft/lbs all day.
Again everyone has an opinion. If you want an engine that has the best of everything internally and 427ci then great. but if you only want 450hp .....