I ordered stuff for my 50 hr service. I talked to my dealer about the discussions here. At first, he said not to change the fluid, but then said that the service manual calls for it - I'd better do it. They don't call for it on the larger machines, but do on the CUTs. So I should. He also said to use Low Viscosity HyGard. He also knew I would buy my fluids from another dealer, so he wasn't just trying to sell me something.
It is probably overkill, but I don't want to screw up a $23K machine to save a few bucks...
My overall guideline is: Do what the guy who is responsible for the warranty calls for. Hard to go wrong that way...