How much percentage of Full Cowling Midoriya was using when he was fighting against All Might in the practical exam? At the last moment when he grabbed Bakugo and made his escape, I am pretty sure he was using more than 5%.
Midoriya already has all of All Mights power, however he is only able to use 8% of it at the moment otherwise it would destroy his body (shown during the early episodes when his limbs would break using the power because he didn't know how to only use a percentage of it, it was 100% or nothing). That is why Gran torino was teaching him about being an egg in a microwave.
It should be 8%. Because, during the training with Gran Torino, Midoriya was able to improve his power up to 8%. Midoriyai has different percentage level moves, you can get more knowledge about them by referring the Wiki. He can increase the attack power percentage but it will affect his body and do a lot of damage to himself.