I'm just surprised that FD have been able to run a 1920x1080 Rift at 75 FPS using a Titan whereas I'm running a 1280x800 Rift and getting 50 FPS to 100 FPS with a 780TI. Unless, of course, they've turned down some of the graphical settings from HIGH which is quite possible.
People are going to have to get used to lowering setting in some games when using the DK2. If your minimum FPS is above 75 in all instances you can try turning some settings up but if you want the optimum VR experience with the low persistence working (no/little smearing = less/no nausea) then you don't want the FPS to drop below 75.
That's not to say you cannot use the rift at lower FPS, your minimum FPS can go as low as 60 but at 60 you will not have low persistence (any FPS under 72 will not have low persistence I think).
Any lower than 60 then you're getting into crappy VR and nausea territory.
When the CV1 releases with it's higher resolution and higher refresh rate you're going to need to run things at a higher res/frame rate which is even more demanding. That's why I recommend making do with the DK2 unless it's totally awful on your hardware so that you can upgrade nearer the CV1's release and get more umph to be able to run it at it's best.