The lower turn brushless you go the more 'savage' it is to drive, so a 4.5, with limited top end electronically will be MUCH harder to drive than a 6.5 selected and geared appropriatly.
A 6.5 motor (any brand) with a decent cpacity Lipo will be plenty fast enough for any UK track, I chose to motor down to a 7.5 at Worksop on Sunday (to improve dravability) and that has a pretty big straight.
Ref Novak motors, they have been around a while but you might want to consider than they haven't been changed much as there is nothing to improve. Wasn't the Novak system the only Brushless system in the A final at the last 1/10th off road worlds?
