Ahh you're scaring me! I got a Vespula and G700, used it for a week but the middle click was defective.. till now it's OK ( didn't use it since the middle click died..)
But the seems to scratch the "speed" side allot, it has allot more friction now that the first day i bought it in... Do you have the same thing ?
You said the mouse stops at a certain point right ? maybe that point is where the scratches are, periodically it get scratched allot and more, so that spot get rough and may not be detected by the mouse ? have no idea....
err, at you're own risk try cleaning the mouse pad with alcohol, or try it on your desk (Maybe not the mouse pad, it's plastic, and has a finish on it, alcohol will remove the finish so it's be as slidy.. just forget alcohol on the mousepad xD).
Another thing, check if there's any dust on he laser, i'm currently using an old canyon optical mouse and there first was some dirt on it's sensor, the crusor at time randomly jumped into direction tilll i put a drop of 70% isopropyl alcohol and then removed it with a tissu which removed the dust. it's there's dust int the sensor try blowing hard into it withought damaging it (err alcohol on 100$ mouse is a bad idea ;P)
And good luck 
