Depends on motor, gearing, track, batteries, etc. When I run 12 cells with a really hot motor, I get over 40 mph - but it's drawing soooo much current, that the battery's heat shrink starts to melt!!!
If I run an average brushless motor with 12 cells, I'll get low 30's mph with comfortable gearing, run-time, and w/o stripping and breaking stock parts.