from my experience, I would use them for different purposes. I have tryed my friends 40 on one of the local downhill spots, I was amazed, the fork is huge but pretty light. it ate up everything I dished out at it, stiff enough for large stuff, but still soaks up rocks and whatever else. I didnt really like the feel of the boxxer WC, but the one I tryed was a lot stiffer and would probably make a great freeride and downhill fork, whare as if I wanted to do downhill only, it would be the 40 hands down.
the company: I've had problems with RS in the past, never had any problems with Fox. either way your getting a nice fork that can handle anything, but look long and hard at service and such.