I don't think that weight loss per se will make you any faster (especially if you have lost fitness due to a forced stay off the bike); The whole thing with being lighter on a bike is the weight to strength ratio that really means something. You will notice it once you bring your fitness level back up, but I don't think you will notice it right away; but go see. The most marked changes you will see are climbing - you don't have to haul so much weight up the hill.