i own a gpx4 rtr, and soon to be a pro,at my local tracks,on short tight tracks,there is bugger all difference between the 2 cars its only on large open tracks that the pro is justified.
for an rtr pull start car,i think that they are the car to get.1.4 hp out of the box.and a great design and build quality.i cant use full power at my track due to massive traction problems,but when it hooks up,theres not many rtr's that will stay with it.
