It'll be off at high speeds or low ones, which is up to you. I prefer accurate in town. There's really only one highway speed I need to worry about, and my speedo errs on the safe side at that speed. There are a lot of smaller speed limits (25mph, 30 mph, 35 mph etc), so I figure accuracy down low is paramount.
Take your tooth count off what you got, multiply by 1.1, and that's your new tooth count. Round per your preference. 33 teeth*1.1=36.3. I'd stab a 36 in there and reclock the housing if needed...
