Go to Powerleaps website, I'm sure you'll find a list of dealers, or put out a WTB thread in the for sale/trade forum here. Powerleap has a user feedback data base with comments and success stories from their customers. You should easily be able to get into the 700+ range with 600E.
Just make sure you have decent ram.
The BM6 had quite a few choices as far as bus speeds go, and mine was very stable. The only thing that might limit you is the CPU voltage limits. I don't think the NEO adaptor gives you any more choices than what is allowable with the motherboard it is being used on.