I take it that you are solely holding over.
If you are using the CMR-W 5.56, then the full usable reticle... i.e. if you wanted to use the very bottom row of Wind Dots (900m) in a 20mph wind, then you would only be able to do so at 1.969x magnification... which is a bit useless at that distance.
At 750m (7.18Mil), you're looking at a magnification of 4.457x to view the whole Wind Dot line at that distance.
Full magnification is going to let you see the full first row of Wind Dots at 400m (1.818Mil).
Regardless the scope is going to be accurate all the way... I guess what you're asking is, is it going to be useful at what distance.
...and the answer is going to be subjective to how good your eyesight is, and at what magnification you're going to need to shoot repeatable accurate shots.
Once you've worked that out, then you'll be able to work out your maximum usable distance.