You can’t gain any if you are CPU bottlenecked.
In this video i played with DLSS Ultra Performance and i still couldn’t hold 120 FPS permanently. I played it in 2160p and DLSS Ultra Performance basicly lowers the render resolution to 720p.
In 2160p it’s like that.
Quality: 2560x1440p
Balance: 2227x1253p
Performance: 1920x1080p
Ultra Perf: 1280x720p