I think a lot of problems on the forum have been related to people not doing a clean install of X2/A. When I installed Win 8 and X2A over the top of XP and 8.53 I was having lots of issues.

If, like me, you're still running an older 32 bit  machine you might find it beneficial to reduce the undo history from the default 128. I found X2A would start to grind to a halt after a lot of editing until I limited the undo history to 16.