For an 8-inch scope, 250x is about tops on an AVERAGE night. Good nights may let you go to the 50x-per-inch limit if your collimation is perfect and the scope has reached thermal eqilibrium. Check out the Sky & Telescope article from 8 or 10 or 12 months ago on cooling of your Newt with well-placed fans.
I do have a 12.5-inch Dob as well as the 10-inch LX-200 and added a fan. It helped. Also, for collimation, a cheshire sight or a laser collimator makes the job much easier.