They used a 308 Win right? I'm chambering for a 30-338 Lapua Improved, so my baseline should be at least 400 FPS faster with a substantially heavier bullet. Next chamber after that is a 30XC, then maybe something based on a CheyTac case.
I recall Kirby saying something along the lines of there were excess case capacity issues using the CheyTac case for a 30 cal, so after the 30XC (assuming I can't fill it up all the way) I'll probably drop case capacity slightly when stepping up to the wider diameter. I don't know yet, that reamer design is still way out there.
There's always the prospect of a 30-50BMG SDSM (Super-Duper-Short-Mag)
Would probably have a COL of about 2.400"