My question is, does the RV-4 need a significant amount of speed on take off?
Yes, relative to trainers or other flat bottom airfoils with light wing loading. About 1/4 of it's maximum speed BEFORE you can begin to lift the front wheels. That is one flaw of sport models. They teach you that raw horsepower beats gravity. In a RV-4 (I've never flown a model of one but it is a "conventional" design) you have to get the wing flying before you can rotate off the ground. Like with most "real" prop aircraft: if you try to lift off before the wings are generating enough lift you will stall. Same with a turn too soon. One wing loses lift as you bank, not enough total lift to keep the plane up, crash.
You don't mention the size or version of your model, so my answer is generic.
The real one stalls at 54 mph and needs 475ft of runway with two people. That's actually pretty forgiving. Models are usually better performing than their full size designs.
[link=http://www.vansaircraft.com/public/rv-4int.htm]RV-4 (the real one) Specs & performance[/link]
If you are taking off from grass that adds drag, also.
It was a g-loaded crash . . .
Going from 30 mph to zero instantly is about a gozillion "g"s. All crashes are loads and loads of "g"s. It's not a lineal relationship, but a 5mph car crash into an immovable barrier (like the earth) puts a 5"g" load on your neck for a fraction of a second, enough to snap vertebrae. Depends on weight and speed.