Assuming USD
A GTX 1660 Super is a very fine 1080p card.
$230 or
$240 for a twin fan model. Actually the twin fan one I linked apparently gets a $10 rebate, so is only $230.
There are cheaper options, or you could even go for an RTX 2060 (non-Super) now the prices have come down a bit, but a 1660 Super is probably as high as I'd really recommend for 1080p 60hz. The 5600 XT is in the same kind of ballpark as a 2060.
It's often not worth buying the more expensive models of GPUs than the cheaper ones, as the prices increase very quickly and there is little room between X GPU and the next model up (i.e. why spend $270 on a 1660 Super when you can get a 1660 Super for $230 or a 2060 for $300 for instance). Also there's relatively little performance difference between Model A and Model B of a given GPU.
In terms of the kind of performance to expect and relative to other cards:
The Radeon RX 5600 XT is a respectable product that has pushed for lower prices and better performance at $300. For that alone, we commend it. The...
www.techspot.com
Your 780 ti would be somewhere below a RX 570 in modern gaming I expect. (that was a guess but seems
borne out by a Gamers Nexus benchmark - this article doesn't actually show a 1660 Super but 1660 Super is almost exactly the same as 1660 ti to give you an idea).