Well all you who pay much more attention to the nitty gritty details of the devices would know better then I (about the position the device takes in the performance/capabilities echelon), but see Pontostroy's results here with a 7790:
Something like this was yesterday. Also this crash happened today. Once I updated x-server from your repo everything looks fine so far. Hopefully the issue is resolved.
As for DRI_PRIME it works fine on my muxless laptop. There is an issue with intel driver in 3.13 (bug report was filled), radeonsi shows an error (another bug report exists) and runpm doesn't work properly (again there is a bug report). Once all this stuff is fixed I can say that open source drivers are in much-much better state than catalyst.