The reason that they recommend 5wt oil ONLY is that the compression damping is pretty sophisitcated, and really dialed to work with 5wt. The fork starts to feel pretty harsh in compression with heavier weight oils. Manitous are highly tunable, so it's possible to use a stiffer shim stack for rebound, but I'd be surprised if it's nessecary. The stock setup should be plently slow on the trail, though it may not feel that way in the parking lot. It's the same with the compression damping. In the parking lot, the adjustment is very subtle. On the trail it's more noticable. I generally use the compression to control bottoming, or increase the plushness of the fork. The rebound I leave relatively fast to keep the fork from packing up.