No cap? Same as (or multiple of) your refresh?

So 120, 240 or 360 fps ?

I cap mine at 160fps with a 144hz monitor. Not sure if thats optimal but I havent noticed any problems

My monitor supports up to 120hz refresh rate. But in quake I used either 125 or 250 fps.

I cant tell you if theres an optimal setting for Reflex, but if you have 120hz monitor, set your refresh rate to 120 and cap your fps at 140 or something and that should be good. At least thats what I'd do

I havent heard anything about optimal settings for the game in particular

For 120 hz monitor he need 125/250/500/1000 max fps. 140 make sense only for 144 hz monitors, on 120 hz it will make unsmooth flickering.

it's not optimal, but you probably won't notice any problem.

What would be optimal?

for most games just capping the fps to a multiple of the refreshrate would be optimal. (in theory just the refreshrate would be optimal)
But quite a few games are being programmed by monkeys who have no idea what input lag means... Which makes the idea less valid, but in general still accurate.

At the very least it will lead to higher consistency, which is the (imo) the foundation of a solid "feel" for the player. As humans are remarkably good at doing delayed stuff.
(the human neural network ain't that fast compared to other lag delays, for instance internet)

the more fps the less input lag

Best advice is to cap at the highest framerate that you can hold steadily. I cap at 500. But yea, you can uncap if you want to shred your GPU.

I recommend testing your FPS and performance on the new version of bdm3. If you can run that map smoothly, you should not have any problem running Reflex whatsoever.