--- UPDATE #2 ---
The dev release of ST2 wasn't any better and I went back to ST3 (again), which still sucked big time. For a while, I did my development on a MacBook, but I missed my dual monitor setup in Linux.
I ended up ditching Gnome3 desktop and using XFCE instead. It is a little too early to tell, but this seems to have made a big improvement. I have experienced one lockup with ST3 in which I couldn't open additional files. I was able to finish editing the open files, close ST3, and reload it OK.
In conclusion, I believe that Gnome3 was contributing to the bad performance in ST2 and ST3. Switching to XFCE seems to have fixed this issue.