I would recommend what I have in my B44.1 to take you to the next level.
A Hobbywing Xtreme Stock ESC and Motor combo. It comes with a card programmer, surge caps, loads of boost controls, up to 8.5T sensored motor and with the timing turned up high, can keep up with a 6.5 on the straight.
Being sensored, it is very smooth and controllable and it will not break the bank.
I can't find the combo but separately from Giant Shark they are almost exactly 130 quid. I got mine from ebay for 99 quid a while back so worth keeping an eye out is you don't mind the wait.
http://www.giantshark.co.uk/xtreme-stock-p-405301.html
http://www.giantshark.co.uk/xerun-bl...-p-407537.html