Did not try GPU passthrough, well at least all settings are default.
Also using duel screens. Had issues with that on a old low power half hight HD 47XX, no isseus using gtx 970. Will be using a gtx 570ti on 4.0.1 rc1 soon if all goes well.
Qubes 3.2 causes almost unusable mouse issue (cursor jumps to left screen edges on each click before input registers with GUI element i am using) but installs fine.