i own a stock surron. its a weird little bike.
it absolutely needs wider wheels, better tires, better fork, better brakes and a 4kwh battery and a better controller (I have almost none of these items), and to be geared down. but these would be expensive mods, like $4k at least.
if the surron had all the above mods, on a tight technical trail ie a trail where on a ICE bike you never leave 2nd/3rd, i do not think it would be possible to run the trail faster than the surron, and it will be way less tiring than on an ICE bike.