So finally RDF handling is done using Soprano (The core of KDE4's nepomuk RDF library). Initially, ferris defaults to using redland in-process for RDF, so the code paths are very similar to what 1.3.x of libferris was using.
But the huge gain is that you can use the nepomukserver or the sesame2 soprano backends if you like. I'd also dearly love to write my own soprano backend, and am bashing out a design for it, but that's a story for another post.
I've run some initial benchmarks, and because much of the speed dependant code paths hit triples directly, giving S+P and looking up Object I suspect I'm not hitting the main benchmarked paths. For example, I've found that some SPARQL queries that perform set based S+P->O lookups run much faster on the sesame2 soprano backend.
Now if only OBS would hurry up, I'd have Fedora 11 packages of ferris 1.4.x available... but in the meantime, the steaming source tarball is on sf.