'06 YZ450F Springs

depends what he understands with "the next step". the owners manual says 0.47 stock, 0.48 stiffer for the fork. in that case you will hardly feel a difference. for me one step is 0.02 for the fork and 0.2 for the shock, means if there are 0.49 springs in the fork it could be a bit on the stiff side (though I prefer stiffer springs with softer valving) but I would give them a try and if you are not satiesfied you can either buy stock springs or if you able to take your fork apart you can soften your shim stack a bit, thats what i would do.

for the rear you have to check your sag, must be many "how to do's" around here