Well, after many many burned up XR2s littering the atlantic, I've finally done a decent run. 1231s from wheel-start to wheel-stop and 20m 17s from wheel-up as clocked by the MET timer. I'm sure that with tweaking and practice, a sub-20m journey is easily possible - it's a case of losing 31s.
A few notes on the configuration:
- Most of the APU fuel was dumped before flight, as was LOX
- No passengers in the XR2 (config file), no payloads.
- Dumped about half SCRAM fuel before flight as it never got fully used anyway, dumped remaining SCRAM fuel as soon as the diffuser doors were closed
Cruising speed was about 11km/s and reentry-profile was steep. Juding when to begin reentry so that you drop out of the sky on ASC is important. I ended up in a 60degree descent down to the base and only became subsonic about 20s before landing. As you can see, pretty much all the tanks were empty at wheel-stop (I even had a bit of fuel left to fire the retro engines on the runway to stop!)