RE: How fast is extreme?
If you're flying 1/2A C/L on 35 foot lines, 70 mph will seem pretty extreme. Me and a friend spent a lot of time in training to get to the point where we could fly out a whole oz of fuel without crashing or falling down. It took some work.
I think it would do all RC Speedaholics some good to go see how C/L speed is done. There are yearly contests in most large areas. There is much that can be learned. On the first trip to watch, the main lesson will be what the definition of what "really fast", really is. This should help to raise your expectations.
Same goes for going out to watch AMA pylon racing in the "Nelson classes".....planes that stay pretty close to knife edge the whole race at 160 to 190 mph.