I have gone that high. Pork butt doesn't care. I take it it's a pellet grill by the temp choices so I would recommend at least an hour (preferably 2) on the lowest setting where it makes more smoke before cranking the temp.
I use a pellet pooper for full shoulder cuts.
I agree with DougE
than anything more than 8# is a twin pack which you will appreciate for dealing with 2 pieces instead of 1 massive slab.
The pooper I can get 250° with some coaxing. The forced air (hence convection oven) does cook the shoulder faster, but I've never noticed a problem. I usually foil pan wrap and into the kitchen oven to finish at the stall.
I use a smoke tube in the pooper so I never start at the lowest "smoke" temp