I think as for compression you can get Accralite pistons of which would be ready from the shelf with 90.93mm or 92.00mm in 9.2:1 of which is the WRC specification.
High Compression engine builds i think are storming in seen some engines and talked to some tuners of which are working with High Compression ratios and there for need low boost pressures as if you think it out High Boost levels on High Compression factor the temperatures in the chamber will be way off (Imagine EGT gauge readings),
But there should be other guys here of which will definetly would suggest your WRC engine build. And they like this kind of setup.