One change in 2.6 that might be making Morphic look like a dog on your P233 is that dragging an entire window and its contents is now "standard" behavior. You might find Morphic much less doggy if you set "fastDragWindowForMorphic" in Preferences to true, so only the window outline is used. (Dragging whole windows is not quite satisfactory to me even on a P2/400.)
My apologies -- I did change this preference, and I will change it back in the future until Squeak gets a bit faster. With Ian at work on Jitter again, and Andreas messing around in BitBlt, I have hopes...
- Dan