I'm currently using Handbrake to compress the Shadowplay files, cutting their bitrate down to ~3000kbps and 30fps so they're about 80-85% smaller in size.
What are other people using?
I'll have a look at Handbrake, I don't have a favorite converter (yet). I hope it has no problems with Playclaw's Fast codec, because other converters I have tried don't work well with it.