Depending on the game, the RTX 2060 is going to be good or decent for Valve Index. However, the minimum recommendation for high-end games is an RTX 2070 Super.
The official minimum system requirement is an Nvidia GTX 970+ or an AMD RX 480+. There’s no official recommended graphics. However, the best experience is on Nvidia 2070 Super and higher.
However, most modern games will give a decent FPS even on an RTX 2060. The question isn’t whether or not an RTX 2060 will be good enough for the Index. The question is, do you really want to use those amazing 144Hz panels, playing modern AAA titles, without having to sacrifice graphics quality just to get a smooth enough FPS? If yes, then you should be spending a little higher and getting a 2070 Super, at least.
It all depends on how high-end you want to go.
An RTX 2060 will suffice for gaming on the Valve Index, to say the least. Expect 90 FPS on the lower end and 120 on the higher end. If you already have an RTX 2060 and don’t wish to upgrade just for Valve Index, it’s completely understandable. Most games will be playable pretty well.
If you’re on a budget and a 2070 Super is too expensive or unavailable, a used 1080 Ti will cut it.
Whatever you choose, make sure you have a graphics card with a DisplayPort. HDMI is not supported on the Valve Index!
I like to get a fan facing me when playing a racing game. Adds the much-needed extra dimension and that oomph. Cheers!