I tried less res I dropped from 2k down to 1080 with basically no noticeable impact on framerate. Similarly messing with graphics options had minimal impact, thats what has me thinking the bottleneck must be CPU rather than GPU.
Yes.
I mean without borrowing and dropping in a 3080 into my existing PC or swapping out the CPU thats the limit of what I can test.
Looking at GPU utilization (with any limiters on frame rate and any Windows/NVIDIA power saving features disabled) should immediately reveal if you have a GPU limitation or not. If you aren't seeing GPU utilization percentages in the upper nineties, the GPU isn't the limiting factor.
You can also. alter the CPU's clock speed. If reducing it produces anywhere near a proportional reduction in frame rate, you are heavily CPU limited.
I can possibly in a couple of months stretch to a ryzen 5 and new mobo if I keep hold of my 32GB of 2400 DDR4, not ideal keeping the slower memory but its still a big jump from my skylake i7 in terms of CPU performance.
DDR4-2400 will be a bottleneck with a Ryzen 5 (the 5600X is likely to remain a great value for the immediate future), but yes, it should still be an improvement.
I'd recommend not spending too much on an AM4 board. I have a MSI B550M PRO-VDH WIFI (which was $80 when I bought it) in my test bench and below about 160w (already well in excess of any AM4 processor's stock PPT limit), or DDR4-3800 with two DIMMs, it's functionally virtually identical to any other AM4 board I've owned (and I've had a half-dozen AM4 boards ranging all the way into the $400+ range). There are certainly bad budget boards, but you can still get a quality board for less than a hundred dollars.
Also, what's the model numbers of the memory you currently have?