I can't answer your question directly. The 17D2 Mk2 is a fine cartridge; it does a lot things very well. The only thing I know for sure is that the Shelter 901 is a better cartridge. It equals or betters the 17D2 Mk2 in every respect - most importantly, the Shelter 901 doesn't exhibit the "color" or "personality" that the 17D2 Mk2 does; in my opinion, the Shelter is a more neutral and more accurate cartridge. I haven't heard the 501 Mk2, so I can't comment on whether it is a worthy competitor to the 17D2 Mk2; my guess (based on my experience with the 901 and my reading of comments on the 501 Mk2) is that it would be, but that's just a guess. I do know that the 901 is in another league beyond the 17D2 Mk2 - but it should be for about twice the price. If you could find a deal on a new or very good used 901, it would be the preferred cartridge; it has deep and tight bass extension, open and airy midrange, and highs that make cymbals sound real. Don't get me wrong, the 17D2 Mk2 is an excellent cartridge, but the 901 is what a cartrige should be - just about perfect throughout.