The key, of course, is to start as a ranger first, then switch to magic-user after you get the ability to cast magic-user spells as a ranger (9th level, Ranger Knight). Because then you can argue, when you reach 10th level as a magic-user, that you can cast all your magic-user spells in armor and when using real weapons. And if someone tries to argue that that doesn't work, well, Secret of the Silver Blades and Pools of Darkness are on your side.
So all you need is a 17 in Intelligence, 15s in Strength, Wisdom, and Constitution, and a lot of XP to become an archmage with 10d8 hit points who can cast in full plate.