Honestly I don't think xfBuild should be used in IDEs, an IDE already has all the information about module dependencies and has a better idea on what to compile.
Currently xfBuild is actually slower than RDMD on full builds (both the D1 and D2 branch). When I further refactor the codebase I'll see what is slowing it down. However on incremental builds xfBuild is faster. It still likes to crash sometime though, so RDMD is safer to use at the moment. Anyway RDMD is DMD-specific, but I want xfBuild to work with multiple compilers (DMD/GDC/LDC/SDC) and linkers.