Depends on how hard you want to ride, I go very hard, crash pretty hard too. But I only dune. I have a full gusseted 89 that now has a bend subframe, all motor mounts have cracked, and some cracks in the crossmembers under the engine. I beefed up my motor mounts to 1/4" steel and added support anywhere I could.
I stock frame can last a very long time. Just take care of it. 4th wide open crashes don't help them stay nice