The 22 series 6 pole motors all have 5mm axles. The biggest one in the 22 series is the 2250 which is rated for max 2500watt's. It's not listed on their site, but I've seen the car version of this motor listed in a webshop. Theoretically that motor should do well in a truggy.

I also just saw they have two 8-pole motors. The 2740 (45*59) which is rated for max 3000 watt's and the 2750 (45*69,5) which is rated for max 3800watt's.