I went to 7k from the 5k my lightning 2 pro came with, and it improved it, a little more oversteer for drifting. I got some 10k too but I haven't tried it yet, I'm pretty happy with 7k, I don't race tho and run on-road.
Hot Bodies Lightning 2 Pro carbon, Mega 22/30/2, MMM, 4s3-5Ah.
Tamiya F201 carbon, Mamba 7700, MM, 2s A123 2.3ah.
Xray XT8, 1518, MMM, 4s5Ah.
Lots of boats. fastelectrics.net
I did run my 10k in the center this past Tuesday and it did change the feel of the buggy a great deal. Before the front end would unload immediately causing slow acceleration (unknown what was in there). Since installing the 10k in the center it now accelerates like it should. If I had the extra time and cash I would get something around 7000 or 7500 and try that also, just to see what the difference was.