I just bought a MSI GTX 980Ti a few days ago after researching that and the TITAN X (and Z). I bought
this one.
The TITAN X gives roughly 15% better performance than the 980Ti. However, through judicious OC, you can get performance on par with the TITAN for many hundreds of dollars less. I won't be OC'ing my 980 as that sometimes causes issues with some games and hardware. However the
MSI TITAN X was 1,700 dollars and I just couldn't justify that for a single card. The 980Ti will run Vive VR effortlessly and a TITAN X gives no real advantage save additional future proofing.
Note: my video cards are MSI and mother boards are ASUS. I've never had any issues with either after three PC builds and recommend them. They are slightly more expensive, but built very well, stay cooler (Twin Frozr) and are quite durable.