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I've got the HEQ5 mount fairly level and reasonably well aligned on the south pole - no noticeable drift in Dec after 10 minutes. But, the mount does noticeably wander back and forth in RA. With a 50mm lens, I might get an 8 - 10 minutes exposure and nice round stars. Through the 600mm scope, even 2 minute exposures show some elongation. (Does a bit better towards the pole). If you're photographing through the reflector (1000mm ??) then I wouldn't be surprised if you have less than perfect stars even with relatively short exposures.
Check you have no movement in declination - I found the drift alignment explanation on the Ozscopes web page the easiest to follow and understand. If it's just movement in RA, then it's likely periodic error.
Also, set your camera for a 2 second delay after you press the shutter - it will give some time for the vibrations of shutter/mirror release to die down too. (I use a cable release too).
I think I'd be inclined to drift align the mount first before doing the star alignment but I don't have the goto capability so I could be wrong there... but I have spent a few hours drift aligning over a few nights to get the best results I can and I don't think I'm getting much better results than yours even though my scope is permanently mounted.
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