Well lets see: I have 4 Grados and 4 Shures. Guess I've been down this road a few times...
Each of my Grados started with spec's alignment (depending on TT/arm) and then got tweaked a slight bit inward to cure the IGD like "sizzle" as the arm tracked toward the center. Once tweaked with headphones and a fair bit of intense listening they are fine
My wife prefers the Grados to other carts in my collection so there is the matter of taste. I would not be without one set-up correctly for any table I own.
OTOH, I have played with the Shures for may hours and between Catman and myself, we have been in maybe a hundred threads about correct Shure loading. For anyone who wants to experiment with Shure (and the M91 is no slouch, second only to the V15) it all comes down to the phono stage. If you can't get your loading up to about 62K or so, you have to use the JICO SAS to get the top end mechanically. It works, but it is not the best solution.
Not saying there is anything wrong with the approach if it's your only option, but a better way to "wake up" a Shure - changing the resistive loading and dialing the cap will get you far more from any Shure body including the M91, M75, V15, or M97.
Back in the bad old days before I had an adjustable phono stage, I used to criticize Shures as dull and lifeless. Once I had the right gear, they all became very pleasant and workable cartridges.
So the OP's original question is more about where he is goings, than about one cartridge or another. If planning to upgrade his phono stage to something with adjustable loading, put the $$ into the Grado and wait on the Shure until you can hear it sing as it was meant to (Shure used to publish their loading requirements, back when yours was built). Save the SAS investment for now and spend it on the phono stage upgrade :thmbsp: