I had quite funny experience upgrading a graphic card.
I had GTX760 and decided to get GTX970. GTX970 is what SteamVR recommends, not that I'm planning on using SteamVR but still.
I did run the SteamVR performance test, on GTX760 it came out negative, though visually the was not any visible hold ups or stutter.
Now when I plugged the GTX970 in, things went horrible. Everything was running super slow, games that used to run good, now would be crawling and the GPU benchmarks would be half of what GTX760 used to be. I was perplexed at first, but then exchanged the unit for another one, and the problems went away - apparently the card was busted.
Now the fun part, despite the fact that nothing ran well on the busted cards, I also did run the SteamVR performance test. Visually it was horrible, skipping frames and tearing. Still the test came out green, and I was congratulated on the fact that I have recommended GTX970 card.
This is quite disappointing but funny to see how valve (or whoever is responsible for steamVR) cheats, and instead of rating the measurements, rating the graphic card model. LOL!