Darki

Yeah your CPU should be fine for 100fps though not 144. That said unless you get a 2080ti you're not going to be getting 1440p 144hz anyways. 1660ti and RTX 2060 are both fine for 1440p 60hz, ignore the 2070 it's a dumb card that nobody should buy, and the 2080 would be suitable for 1440p 100fps. If you want 1440p 144hz you'll need a 9700k at 5ghz and 2080ti...so yeah I'd go 100fps lol. 

For 1440p 60Hz:
Get a 1660Ti or find a good deal on a used 1070 Ti. Just depends on what you're comfortable going with.
1660Ti's MSRP for around $280 (the EVGA XC Black triple slot is a good card, I've tested one before), 1070Ti's look to be around $180 to $310 on ebay (which is roughly the same price spacing as 1660Ti's). 
 
Both perform pretty similarly, though the 1660Ti might be just a little bit better.

Your CPU can last you a little while longer, I reckon (especially with an OC). But a 970 is not going to cut it for 1440p, let alone at 144Hz. 
A 1070 or 1070 Ti would suit 1440p 60Hz pretty well, but if you want 144Hz you should look at a 2070 or 2080. 
 
You could upgrade to Ryzen later this year after Zen 2 comes out, but for now I'd get a GPU and see how it performs.

I have an overclocked i7 4770k and 165Hz 1440p monitor. 
While the CPU is starting to show its age, it can still handle at the very least 100-120FPS in the more demanding games. 
 
Definitely upgrade your graphics card first, your CPU will still be fine for at least 1-2 years unless you absolutely must see 144FPS+ in every game.