I just saw an article in RC Driver about these motors and I'm now planning to put one of thesekits in my wife's EMaxx. Personally, I would rather go with twin 700's than one 970. If you do a single 970 with the 40T pinion that they send you, you're essentially not upgrading too much from the twin 550's.
I'm not sure if I want twin 700's or twin 970. They say the 970's require high end Nimh packs or 20C Lipo. I have yet to make the jump to Lipo with the exception of my Micro DT but I think that may be something I do this year finally. For the money, the twin 700's are probably the best buy on the market. Actually, now that I think of it... the 700's would probably be better since I'm dealing with the old EMaxx, not the new EMaxx with the brushless ready tranny.