[Fletcher]

FWIW... I have never been a 421 fan on any guitar at any period in the evolution [or de-evolution depending on your perspective] of the 421. It can work sometimes in conjunction but I always seem to end up with this like 3kHz "ice pick in the forehead" kinda thing when I try 421's in general.

One thing I would definitely suggest is for you to get the cabinet off the floor. When you have something like a 4x 12" cabinet on the floor it couples with the floor and gives you a false sense of bass... which means you have great bottom in the room... but not such great bottom coming out of the speakers... and that's where you're putting your microphone, right on one of the speakers... no?

If you can get the cabinet up in the air a bit... on a road case or a coupla bar stools you'll be able to hear exactly what's coming out of the speakers [it'll be on ear level] and you'll be able to adjust accordingly.

If you're a fan of the 58 on one kind of guitar recording then it'll probably work just fine on the other kind of guitar recording you're doing. Again, in the FWIW world... I usually prefer small diaphragm FET condensers for loud / distorted 4x 12" kinds of sounds or a ribbon before lg. diaphragm condenser mics... but that could very well just be me.

There are a billion and a half different mics on the planet these days... there are several el cheapo Chinese condenser mics that should be able to handle the task of "loud guitar" without a struggle... so if you're hell bent on trying a lg. diaphragm condenser you may want to wander on down to the Banjo Mart and pick up something that seems to have some balls to it [careful of the overly bright / harsh top thing that many of them provide as that does NOT go well with GTR's... try to find one that is less "bright" than a TLM-103 and you should be on a path].

From my limited experience with them I would advise you avoid the Chinese ribbon mics for another few years... eventually they'll get it figured out and kill off the remaining US companies that make ribbon mics... but until then [from what I've heard / experienced] it's shit product, so let someone else fund their R & D budget while you make records.

Peace.