what about a big outrunner motor? in general high efficiancy, and lots of torque which is recommended for such a big car.
there are many companies around, producing high quality outrunners.
these guys here
http://www.torcman.de/ have for example a monster which can pull up to 4000 watts...
or e.g. flyware, I just have ordered one of their large inrunners (8pole), as the feigao-clones' magnets break...
here's an outrunner that takes up to 45 volts:
http://www.flyware.de/wde/erp/shop.php?navid=4
65 mm of diameter should provide some power
they also have nice motors (some are inrunner-looking outrunners), but probably too small:
http://www.mvvs-electricmotors.de/index.php