If you upvote say 20 posts a day at full strength, your VP will never reach 100% but it will stabilise at a certain percentage. Each vote you do will be worth less but you can vote as much as you like at 100% really. When I was a bit more active a month ago I used to vote about 20+ times a day and my VP would always be 70-75%.
I tried to do so (just about 20 upvotes), but for some reason my VP was declining and declining until it dropped below 50% and I had to take a break for a few days so that it would recover.