MM or MI Cartridge?

The Grado is a safe bet! You will have to buy it and try it in your own system. Too many variables in other users’ systems to depend upon anecdotal opinions. Cartridges, like speakers, vary widely in sound quality. What pleases someone else may not please you!

Way back in the Days of Yore (late 70's) I had to choose between two cartridges - an MC and an MI type. The GAS Sleeping Beauty and the Grado Signature One. Both cost the same - $240. I went with the Sleeping Beauty mc cartridge - though I had to put it aside for a few months until I could afford a Mitchell Cotter SUT. The Sleeping Beauty gave much pleasure, though the Signature One would have probably served just as well! I just didn't want to pay so much for a Grado cartridge. The lowly Grado FTE ($15!) was praised by Harry Pearson. The Signature One ($240) was Grado's premium - and most expensive! - cartridge. I shake my head in disbelief when I read of a Grado Epoch costing $12K! 

Soundsmith makes a strain-gauge cartridge. This type does not use an RIAA network/phono stage. It does the equalization mechanically. It can drive a line stage - eliminating the phono stage. I listened to the Panasonic strain gauge at a friend's house. It fed the line stage of a Marantz 7 tube preamp into a pair of Futterman H3aa OTL amps into Quad 57's. I was impressed! Soundsmith claims their strain gauge cartridge is a superior improvement over the Panasonic.

I remain an mc cartridge fan and user because no mm or mi type I have tried can equal the "liveliness" and detail retrieval of a good mc cartridge. Even the lowly Denon 103 is capable of astonishing sound quality! Why don't you consider an upper-tier mc cartridge like a Miyajima Madake? After all, that Ortofon SPU is rather long-in-the-tooth for an mc design!