Benefit of low output moving-iron Grado ?

Thanks, Photon46 for the valuable info; very relevant. In fact, since my initial writing I realized that an operative consideration in all of this is the phono pre-amp. I looked around a little and read about the Grado Ph1 MM/MC preamp which seems like a deal and would theoretically be pretty well matched to a Grado cartridge. Since you also mentioned the fallibility of theories, perhaps someone could vouch for the particular combo of Grado Master .5mv and Grado Ph1 phono preamp? I live a distance from anywhere I might be able to audition stuff (and we have no car), so I rely a lot on research on the web.
Another side question I've got is about cartridge setup. I see that there are two screws on the top of the tonearm which go into the cartridge. If the cartridge I buy weighs exactly the same as the old one, wouldn't installation be as simple as removing the wires from the old cart, unscrewing the screws, and installing the new one in the same way? I wouldn't need an entire setup procedure from a professional, would I?
I have to admit I've never even heard a low-output cartridge and I'm going on research alone that it might be something I'd like. And with Needle Doctor's deal on trade-in cartridges along with the still-affordable phono pre-amp upgrade, it seems doable and worth the potential error in judgement. I could always trade-in the Master Standard for a Sonata Reference for the additional $450 if I'm unhappy, I suppose. And it's not like that's small change for me either, that's three weeks salary! I guess I suffer from the bug like anyone, and I find great enjoyment in listening; always have. Thanks for the heads up on the "cohones" issue! Very glad to have gotten these responses folks, thanks....

No professional setup needed! Just swap cartridges!

I have no experience with modern Grado cartridges. However, I do own a Grado TLZ, which was one of their early efforts at making a low output cartridge. (Incidentally, I don't think the Grados are classic moving iron types; I think they are "induced magnet" types, altho that is a distinction without much difference.)
The TLZ was a great cartridge in its day. On the other hand, I also don't think that all high output cartridges are inferior to all low output ones. You have to take this on a case by case basis. I have several MM cartridges that compete with any high dollar LOMC cartridge. Bottom line: you would have to try both versions of the Grado Master and make up your own mind. My opinion: given the rest of your system, you would probably be just as well off to go for the less expensive option, which I guess means the high output version of the Master. What Photon did, buying two new phono stages to try to make his low output cartridge sound OK, is nothing short of heroic, and expensive.

The Master is a $1000 dollar cartridge. What Grado are you talking about? I thought you said Sonata low and high output!

Swapping the Sonata for the Master should be pretty painless as far as setup goes. It could need rebalancing though, as there are fewer turns of wire in the low output Master and the older Sonata bodies were a variety of Mahogany whereas the newer model 1 Grados are denser Jarrah wood and probably weigh more.

If I were buying another Grado, I'd think very seriously about getting the VPI 1.5mv output version, seems likely to be a good compromise that splits virtues of both versions.