I suspect 520W may be a little low for a R9 290, but should be fine for the GTX970; don't they recommend 450W for that one? Which accounts (in part) for liar-labels? Mine only has a single 8-pin PCIe power connector, which means the card can't be pulling any more than 225W to remain in-spec for PCIe.
Second the Define R4. That's on my [very] Short List if I build another ATX system any time soon.