I have been playing my GK 115 8 ohm with an Ampeg pf500 and loving life for the last few months. I have now decided to add another 115 to the set up. One can be left at my house and the other at my guitarists for practice. When it's needed for a larger show I can combine both, but otherwise travel back and forth with only my bass and amp. The problem is that my pf500 has crapped out before it could be used, so now I'm on the hunt for another head and have it somewhat narrowed down. I have been looking at the GK mb 500 and 800, in comparison to the 700rbII. I'd like to know if anyone has experience with these combinations. Is there a noticeable difference is sound or power between the mb 500 and 700rb? And secondly, should I suck it up and move up in power to a mb800 to power this duo?