You really can't go by distance, you have to go by time and output. A 20 MPH wind (from almost any direction except square at your tail) is going to increase your energy output, whcih means that you need to increse your energy input.

There is also the rate of energy output to consider. You can bonk just because you body can't process the fuel fast enough. You might consume plenty of calories, but if they're all in a form that it takes your body too long to convert to glycogen, you're screwed.

Been there, Done that. Pain is a good teacher, isn't it?