A larger motor would allow for more instantaneous torque, which would draw more current. So it would be harder on the ESC. You'd want to make sure your ESC fans are still kicking. Or upgrade. You may also want to consider the negative side affect of a huge addition of weight from the larger motor.
You would also need to consider installing a massive pinion on the motor to compensate for the lower kv of the 6s motor. i believe the size limit is a 27t on the v3 blx trucks. So keep that in mind.
That said, I've been running a 2650kv 4068 size surpass motor for quite a while on a granite and a big rock with good results. I still can run into overheating issues though if I run it hard. The stock motor heatsink is crap. Remove it and get a clamp on style motor fan mount so the air blows straight across the motor can. That should help.
Another good option are the 3670 sized rocket/surpass motors. You can pick them up in a variety of KV, and if you get the finned can style, they are really easy to cool with a fan mount and fan.
