Grouped objects also have impact on this: when at high zoom level, if you have some objects grouped and experience the slow down, ungrouping them gives a boost.
Sometimes the slow down is so heavy that I can't double click on objects anymore, as the two clicks (regardless of how fast I can do them, and I'm fast!) are always managed as two single clicks. Zooming out decreases the slow-down and double click restarts working.
Grouped objects also have impact on this: when at high zoom level, if you have some objects grouped and experience the slow down, ungrouping them gives a boost.
Sometimes the slow down is so heavy that I can't double click on objects anymore, as the two clicks (regardless of how fast I can do them, and I'm fast!) are always managed as two single clicks. Zooming out decreases the slow-down and double click restarts working.
Windows XP SP3.