Personally, I feel the Shelter 501(0.4mv) is in every way as good as a Helikon, but has some differences in sonic character, and sounds more like the Koetsu sound than the Lyra sound. I feel the Shelter 901(0.5mv) is definitely ahead of the Helikon, but the 901 has less of the Koetsu "magic" than the 501. The 901 is a more "straight ahead" type of cartridge, but it has lifelike detail, and great bass response. I don't know about the 90-X(0.6mv), except what I have heard said by others, which was that there was a small improvment over the 901, but enough to be significant. I also agree with David(4yanx) that the ZYX R-100 Fuji or R-1000 Airy are superb cartridges that are equal or possibly better in certain areas than the Shelter 901.
I have not heard the Titan, so I cannot comment on that.
I think that the Koetsu Rosewood Platinum is a very fine cartridge, but it has a very low output, and you'll have to use your transformers for that cartridge. From what I've heard, the Koetsu cartridges are much less expensive in Japan, so they could be a very good deal for the money.
All-in-all, it is kind of a nice predicament to be having to decide between all those super-good cartridges. I am envious.
I have not heard the Titan, so I cannot comment on that.
I think that the Koetsu Rosewood Platinum is a very fine cartridge, but it has a very low output, and you'll have to use your transformers for that cartridge. From what I've heard, the Koetsu cartridges are much less expensive in Japan, so they could be a very good deal for the money.
All-in-all, it is kind of a nice predicament to be having to decide between all those super-good cartridges. I am envious.