would it be louder if i do dual 2.5" or would dual 3" be ok and i wont lose power

 

you dont really loose power, it moves the powerband up, so its still there but its higher

 

The dual 2.5" will be the best for your application. The dual 3" will make it alot deeper tone and may even make it quieter than the 2.5". I have Dynomax ceramic coated headers attached to a full TTI 3" dual aluminized exhaust with H-pipe and 50 series Flowmasters, but this is on my Roadrunner which can and does make full use of the larger size. It made a huge difference in not only the sound, but the power and throttle response as well, and that was going from stock exhaust manifolds with 2.25" stock dual exhaust and stock mufflers. But this was also a mildly built big block versus a factory built lower compression smaller big block.