Vega uses way too much power. A GTX 1080 should work but they are way too expensive. You could get a single GTX 2080 Ti for considerably less. As not many games are well optimized for SLI. The single 2080 Ti will do better in most titles. Usually it is better to have one great card rather than two mediocre cards. Same goes with dual 1070's you could get a single 2080 instead. SLI/Crossfire never took off so most game developers ignore it.