RE: twister xtg pro?
the ESC is 3s lipo ready. dont have to mess with the fan or anything.
as for upgrading the bandit?
they are a fairly tough chassis. but you would be spending over $100 on the bandit to get it to full VXL spec.
the vxl bandit metal gears in the tranny, stronger driveshafts, a waterproof 2075 high torque steering servo, larger wheely hubs and bearing.
by the time you upgrade those parts and buy a VXL esc and motor its gonna cost a fair bit.
as mentioned by another, the esc and motor in the twister can be dropped into the bandit! so if anything broke on the twister you could run the BL system in the bandit while waiting for replacement parts.