Be sure to check the high speeds visually, just open the back, set shuttter speed to 1000 and watch the curtains as you shoot the sky. I'd do that for any vintage focal-plane shutter camera, not necessarily Pentax. If part of the shutter doesn't open, avoid that speed. Check 500 and 250. Most of the time I find 250 is the upper limit, then I simply avoid shooting above the highest reliable speed.