I routinely use a 90mm MAK to guide with. I keep the exposure times low and have not noticed bloated stars. I use an XY shifter to pick a nice star on the screen and guide on that. I find that for a 2500mm scope the mak guides very nicely but I must state that I use an integrating video camera (Watec 120N+) with a TVGuider.
I think that from what you are describing you are getting star bloat and that you either should use a dimmer star or drop the guiding rate to 0.3 or 0.5X siderial which may help. Maybe guidemaster would be a better choice of program to use with a DSI.
Regards, Allan
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