They don't correlate, because the lag from each one won't align exactly with eachother and both are very inconsistent (even when fps is capped). The simple explanation (as long as your fps and hz are not the same, and both aren't extremely consistent, which fortunately isn't the case) is you add delays together to find the max delay (which is a worst case with the frame and poll being at just the wrong time), so doubling one and halving the other won't give you the same result.

So, using (1/fps + 1/polling)*1000, 120 fps + 1000hz would have a maximum delay/input lag of 9.333 ms, while 240 fps + 500hz would have a maximum delay of 6.167 ms.

Of course, if your mouse works flawlessy at 1000hz, there's no reason not to have it at 1000hz, which at 240 fps would bring the maximum delay down to 5.167 ms. And the minimum would always be whichever's slower of the two, so your minimum would be 8.333 at 120 fps and 4.167 at 240 fps as long as your polling rate's higher than those. 1000hz also has the added benefit of the delay being half as inconsistent (+/- 1ms instead of 2 for 500hz), so you really should go with that.

thank you. i asked because after switching from 120 to 240 fps the smaller max delay is harder to adjust to making it feel like a faster sensitivity. i guess i just have to get used to it