Get a Nady RSM 5. It's a great little ribbon and for under $100 it'll be well worth the money and will let you know if you want to buy a Royer or Coles on down the line.
The AT4033 is also a great mic for guitar amps when you want to capture ALL THE DETAIL of the amp. It can get a harsh, but it can also get really well defined. I would never use it alone for guitar cab, but have often used it for bass and guitar cabs where I needed some definition and clarity, and paired it with a dynamic or ribbon for meat.
The MD421 that you wanted is also a nice option. however, I'd tend to use it instead of a 57, not so much with it. But that's just a personal preference. I did go through a phase of using the sm57 and i5 together on cabs. The recordings sounded pretty good, but I find I like the broader options of combining two or more different kind of mics (condenser, dynamic, ribbon) on a guitar cab.
However, with heavily distorted guitars, I find you either need to record DI and use some amp sims or use some really nice preamps. In either case, what you're looking for is some clarity and precision in all that distortion. I find it hard to get the guitars to really cut through a busy mix when I am just using mic'd guitar cab tracks that I recorded with fuzzy or slightly veiled preamps. But great preamps are expensive, and a low cost work around is to use a DI track and amp sim and mix a bit of that in with the rest of the guitars to bring back some of that clarity.