OK, cabs... I'm looking at getting the epi ul410, does it make a difference with the 728 if I go 8 or 4? If I go 8 and add a second (in the distant, distant future when the credit card cools) I'd be running 2 cabs at 4 and if I had 2 4 ohmers I'd be running at 2. Is there any difference in sound or how hard it runs the amp? thoughts? does it matter?