I was pleased to see another beta tester online yesterday playing with an off the shelf laptop. It was newly purchased and had a GTX970 on board. He seemed to be very pleased. If you were asking for minimum requirements it definitely has not been established, but there have been some recommendations about amount of dedicated video memory ( 1 GB will work, but if there is a lot of benefit in going higher from 1.5 GB up to 4 GB ). GDDR5 memory, and various other video card specs like memory bandwidth are also top considerations without mentioning card manufacturers by name, or setting a price tag on good performance.
Regardless Bortas, just about every system you can imagine will get pushed by the available graphics, if you decide to enable it. So, it is wise to keep testing and reporting with what systems you have before trying to upgrade too soon.
Kudos HTC smooth running for the most part so far.