Interesting.
I have an old Ford Industrial TLB from 1963. Going thru ebay, I got a bit of period literature for it. The specs for the operation of the hydraulics that power the loader and hoe specify lift capacity and cycle times for the cylinders at a certain engine rpm and oil temperature. Yeah, they actually printed something in the sales literature that is what I consider hard data! Weird, but true! They list it as 160F. And it does get pretty dern warm.
Given the amazing advances in lubrication technology in the past 43 years, I wouldn't be too concerned at 160F or 190F or for that matter even 210F. Much over that and I'd be afraid the seals would start to harden and degrade.
jb