Air filter and exhaust - timing

I just put a free flowing air filter in my 92 Fleetwood and installed a Magnaflow Camaro exhaust. Now i've got two chrome tips just peeking out the back bumper on each side. Looks great. And the sound is perfect! A little rumble, but not loud. Sweet!

Though I haven't really noticed much of a performance increase.

I've heard of people advancing timing from 10* to 14*, would this make a difference?

Also, I removed the tubing that goes from the airbox to the fender. Would cutting the box open more give me better flow, or does the little opening that's left flow enough already?

Thanks,
Shane.