80-days supply pool is a bad idea. No additional cost for SR is also a bad idea. Unless other changes are made to balance this properly, I cannot see how the new values would help us to improve the game.
80-days pool means that amphibious invasions become extremely easy for the player. In fact, with a big offensive, one could liberate France, Netherlands and Belgium without capturing a single port! Just think about it - 30-days pool is already too high for the purposes of amphibious invasions, that's why some mods reduce the pool to a 15-days one. 80-days pool would make the situation much, much worse and a potential slight boost in AI efficiency would not be enough to counter that.
Also, this change means that encircled units would run out of supplies at a far lower pace, which is not desirable at all. I doubt that we want to see units that can be supplied fully for almost 3 months while being captured in a pocket.
Moreover, with the new uber-pool units stationed overseas would demand much more supplies than they really need. This would actually create problems for the AI, because it can only check how much supplies is in the capital, not overseas. Therefore, the AI would produce more and more supplies, which it doesn't really need, so it would, in fact, waste more of its IC. Also, while the player would be smart enough to stop sending convoys to places where supply stocks were extremely high (80 days is almost 3 months!), the AI would keep sending them, giving the player's submarines more targets.
ATM strategic redeployment is only balanced because of the fact that it draws 2x more supplies (and incurs an attack delay), so it is isn't really that beneficial to use it all the time, especially when the distances are short. If we change this so that SR units will draw 0.25x supplies, SR will be far, far superior to standard movement. Remember that SR units require 0 fuel - now they would also require almost no supplies! There are no railways and locomotive in HOI3, so your SR potential is not limited in other ways.