I have the Vive and my set up is:
CPU: AMD Phenom II 3.4GHz
RAM: 8gb
GPU: Radeon r9 270, which is 4,000 points lower than the recommended card (GeForce gtx 970) according to videocardbenchmark.net.
It ran Google Tile Brush, Fantastic Contraption, and Universe Sandbox fine (Universe sandbox would lag if too many items were spawned).
However, Job Simulator lagged about every 10 seconds and crashed every time after a minute or two.
So it depends on what games you intend to play, but I wouldn't cheap out on the graphics card. If you want to play demanding games (and even more demanding games that will come out in the future) unfortunately you're going to have to spend $300 or more on a gpu