I knew there was something I forgot earlier! This is the track fully layed out out on the board:

The gap is where the ROCO geometry has let me down, and will need filling in with some flextrack. Luckily I have some PECO crazy track that I can disguise by overfilling with ballast so you can't see the sleepers. It seems to have the same profile as ROCO track, so there should be no jumping of trains.