One of my favorite quotes is from SW fly rodder Lou Tabory;
"When the wind is in your face, the fish are at your feet"
I seem to fish in the wind a lot.
It's either deal with it or don't fish... so I deal with it.
When the wind is up to and over 15 knots, I break the 10wt out and for me, wind in the face, I'd say 50' is realistic but I've never had the occasion to measure.
Two seasons ago, on our annual trip, we had 20 knots sustained with gusts to 40 for a week straight. That was an occasion to learn some new spots to fish in the lee. Even fishing with the wind over the non-casting shoulder was tough, mostly from all the spray. We toughed it out, fished all day, every day, fly rods only.
When the wind is up and there's a lot of chop, I find you can get away with a much shorter leader than when the surface water is flat
But personally I have never fished flats when the wind is at 20, I'd look for some place with a bit less exposure
I was at a casting clinic with Bob Clouser a few years ago and I asked him 'what's the best way to deal with a stiff breeze over your casting shoulder ?'
He looked at me and with a one word answer said