It'll depend on the specific titles you play, the resolution & the GPU it's paired with.
1080p with something like a 1050TI... I wouldn't expect a whole bunch of improvements.
Paired with a 1080TI on the other hand, and the gains could be substantial.
I would suggest looking up benchmarks for the titles you play - although for aging hardware like the 3570K you may be limited to Youtube "benchmarks".
Each title will vary quite a bit, depending on specifics.
For example: The Witcher 3.
Mid 40-70FPS on the 3570K (@ 4.2GHz) and paired with a 1080.
https://www.youtube.com/watch?v=xChZ0Hp2glI
Vs
2700X + 1080, same settings.
https://www.youtube.com/watch?v=EhoEAE0paec
65-80FPS, but more stable IMO.
PUBG
50-110FPS (probably 70ish average) on the 3570K / 1080 / High / 1080p
https://www.youtube.com/watch?v=3UPVKIFcsJg
Vs
100-150 (~125FPS average) 2700X / 1080 / Ultra / 1080p
https://www.youtube.com/watch?v=GDj-3OcxTnw
Of course, there has been optimization patches between the postings of those videos - and they're not direct apples to apples...
So there's two titles..... one with ~15% "gains" vs another with ~80% gains (and higher settings).
Totally varies game to game, GPU to GPU and resolutiion to resolution.