That'd due to RAM and HDD cache (note the "reading virtual memory message). :D I can go above 15 million polygons and undo takes maybe 2-3 seconds, and the framerate is great (8gb RAM, q6600, etc.). For memory, make sure in Preferences memory isn't set to 256, since I have 8gb, I max it out at 4096 or so (I think that's…