Do you want a new, current graphics card or a used, last year's graphics card?
I'm currently using a used EVGA GTX 770 in Thunderball. It doesn't require the Nividia drivers. (I've not updated my build description as it hasn't really changed anything in the OP.) The GTX 770 is about equivalent to a AMD 280X.
I would stay away from the GTX 10x0 cards at the current time as the current Nvidia drivers are causing some users problems (see the Graphics forum section). A used GTX 970 is also a good graphics card, but it also requires the Nvidia drivers, but I haven't read of any GTX 970 user having problems with the latest Nvidia drivers.
BTW, I'll update Thunderball to High Sierra 10.13.4 later next week after I return from Spring break.