I obviously dont know your stack so this might be useless if you're heavily invested in AWS - but you might want to try scaleway, you'll definitely get more bang for your buck in terms of performance
I'm actually up for that, if you can suggest an alternative way of doing this (ideally using LXC rather the instances), that would be great. Target is 'always on' instances and reduced cost.
We've been having good success running desktops as docker containers, scheduled on Mesos using cheaper GCE machines. We use TurboVNC as it has a built in Javascript VNC client too.