Anything you are willing to spend money on: Modern games basically never bottleneck on the CPU.
This is no longer true, several modern game engines such as CryEngine3 and Lumberyard extensively stress CPUs.
The days of GPU being the only bottleneck you worry about are long gone.
As for what GPU? That's relatively easy, what do you want to play on it? Although I'm not too aware of the price equivalence, I can second the call for a GTX 1660, it's a solid card that will be able to make use of the system.
You'll never run Star Citizen on it, but then again, I doubt anyone is going to run Retail Star Citizen, ever. :-P