As long as you choose an availability zone that is closest to you when setting up the box, the latency will be minimal. In our experience with using Vim on our boxes, it was not a big problem. Emacs will run just as fine! (We aren't taking sides, I used Emacs a lot when I was doing Scheme.)
I must say I am really impressed by the speed and performance of SublimeText 2. If they can get the vintage mode (vim mode) right, I might really consider switching. At the moment it's nowhere near perfect.