This reminds me of an idea I saw somewhere for Pewter Ferring super-soldiers. Basically you’d just have them be constantly filling strength, and then put them through a normal training regiment. They’d (theoretically) increase in strength while also filling their Metalminds. So eventually they’d be at normal person strength, but only a small percentage of their own because they’re still filling. Then, stop filling, and boom, super-soldier. Also they’d have a ton of strength stored up at that point, so if their default is already super strength, imagine them tapping all the strength they’ve been storing up.