I don't know the wind speed but I recall a verrrrrrrrrrrry long day touring in Belgium back in the 80s. Belgium is about as flat as you can get but at times I had to stand on the pedals, in my lowest gear just to keep moving forward. I was just there for a few days and even though I toured in a circle, that damn headwind span around ahead of me. I think that was the only bike tour I was ever glad to finish. I got hit in the chest by a bouncing coke can and on the knee by a cartwheeling wooden sandwich board. I saw it coming from about half a mile away and just knew that whatever I did, it would still catch me. I resolved to hold my line and let it do its worst. Then at the last moment I lost my nerve. I zigged but it zagged and caught me a pearler. Dang, it hurt.

More recently, last spring here in Colorado I spent almost 2 hours riding 10 miles into a headwind, then turned for home and at one point hit 43 mph, sitting upright and barely pushing the pedals.