I can almost guarantee you that without a hefty tailwind you are not going to push a 50/13 at 80 rpm. You can't go faster just by havingn a higher gear, neither can you get in better shape by pushing a high gear at low revs, for reasons related to both your body and the mechanics of a bicycle. Racing cyclist go at high rev's for a reason. Even among elite cyclists there are very few who can push high gears successfully.

100 rev's is great, but if you're going at 80 now getting up to 90rpm will be a big help. That is what will get you to your goal, and eventually to the point where you actually need that 13 tooth cog.