I've got the 5700 in my B4 and on 6 cells, it'd be too much on a track IMO. I didn't run it with the GPS on 6 cells, but on 9 - IB3800 cells (unmatched and unzapped), I GPS'ed it at 52.2mph. Here's a couple of fun pics we took today while we had it out running:
http://onelouds10.com/rc_pics/IMG_2306.JPG
http://onelouds10.com/rc_pics/IMG_2307.JPG
http://onelouds10.com/rc_pics/IMG_2308.JPG