If there actually is a higher server load, which I still doubt, it would only be caused by clients who actually can render those higher FPS. I'm guessing a whole lot of players will not get to those numbers anyways. Capping the limit will annoy the few players who actually want to increase their FPS (and know how to, let's not forget that there are a lot of people who aren't that familiar with tweeking their CFG).
Maybe you should just give it a try and see if the server suffers from it or not? It's easy to reverse and I'm sure you'll make some people really happy in the process
I don't have time for gaming these days so a come back won't be possible haha. (If anyone catches me gaming -> it's not because I have time, it's because I have the bad habit of procastinating, don't encourage me )