I guess I'll just have to test it out. I generally agree a full length 3.5" system would be freer flowing, but dual 3.5" is way more than I need. You really have to be putting down some serious power levels to even need dual 3". That's 4 digit power territory there. This is why I'm sticking with 2.5. my combo as is will do very good to go north of 475 at the crank.
I am currently running a 3 1/2 system to the back bumper. Pieced together with straight pipe and mandrel bends. Huge mufflers! It's probably too big for this 500hp 440... but it was built for the next combo, 522" nitrous motor.
But heck, I ran a 3 1/2 system on a small block too.