The quadzilla is like the banshee.Port work amongst other things can make or break it.
Get the wrong port job,pipe,etc...,and it will run like junk.
I've raced some quadzillas that didn't impress me a whole lot but if they had a great builder do the work then they can run pretty strong.
I have heard alot of good things about Dr.Q.
Something else.In the videos,you are racing on grass.For a banshee you might as well be on ice probably.I bet traction is one of your biggest issues.