It's kind of hard to tell from a pic, but I think I'd go with the 5700 for nimh. The 7700 might be to much and you'd have trouble getting it to hook up. Although I do like the 4600, that track looks like you could use the 5700.
the problem we have is when it get's watered it good for about 3 heats then dry's out real fast (good ole virginia clay:035: ). we normally run 1/8 scale buggy's but there has been alot of electric interest lately so now we're running both. ya traction is alway's changing but it keep's ya on your toes with the throttle. i think i'm going to have to do a little testing. thanks.