You might ask Dallas Robinson what he thought his chances were once he gained back–after he got injured, etc.–the weight he lost to sprint last year.
I went from about 215 to 195 at 6’4" over about 2 years after I decided that I wanted to weigh what Asafa weighs. There’s no doubt in my mind that losing the weight made me faster, but it is very difficult for anyone to separate weight loss performance effects from training performance effects.
The key, I think, is to make a longer-term commitment to doing it slowly. If you keep the weight loss to not more than about 1 pound per week, you can do so without losing strength and without missing nutrients like protein that you need for recovery from the track.