For 1080p gaming, GTX 1660 Ti will do fine with average FPS around 100 (depending on a game). But if you want your average FPS to be near 144 with maxed out settings in most modern games (since you have 144Hz monitor), you'd be looking towards RTX 2060 Super,
GTX 1060 3GB vs RTX 2060 Super, comparison:
https://gpu.userbenchmark.com/Compare/Nvidia-GTX-1060-3GB-vs-Nvidia-RTX-2060-Super/3646vs4049
pcpp:
https://pcpartpicker.com/products/video-card/#c=446&sort=price
Note: with RTX 2060 Super, a good quality 600W range PSU would be needed (if you don't have one already). Any Seasonic made PSU will do fine, e.g: Focus 650 (80+ Gold), Focus+ 650 (80+ Gold), PRIME Ultra 650 (80+ Platinum) or PRIME Ultra 650 (80+ Titanium),
pcpp:
https://pcpartpicker.com/products/compare/WrNypg,qn7v6h,7fndnQ,fnjJ7P/
Warranty wise:
Focus: 7 years
Focus+: 10 years
PRIME: 12 years (includes all PRIME models: regular, Fanless, AirTouch, SnowSilent, Ultra)
All 3 of my PCs: Skylake, Haswell and AMD are also powered by Seasonic. Full specs with pics in my sig.
Also, PRIME Ultra 650 (80+ Titanium) is the best 650W PSU money can buy at current date and with it, you'll get the highest efficiency (92%), tightest voltage regulation (0.28%), longest hold-up time (30ms), lowest ripple noise (14mV) and longest warranty (12 years) there is. Fully modular cables and toggle-able Premium Hybrid fan control too.
specs:
https://seasonic.com/prime-ultra-titanium
review:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=536