I have not heard XV-1t either but have listened to Onyx, Rosewood and XV-1s in my system. Nolitan's description of XV-1s is very accurate. Koetsu as a whole offer smoother, richer more pleasing midrange. However Onyx offers more extended top and much better control bottom than Rosewood. I found Rosewood excellent with vocal, piano, small jazz but could not compete with XV-1s in large symphonic work, rock/pop so I think XV-1s is a better all around cartridge than Rosewood, at least in my system. However, I would take Onyx over 1s. Unfortunately, I have absolutely no idea how it would compare to 1t though.
As a bonus for Koetsu, I find Koetsu cartridge in general to be one of the quietest if not the quietest cartridge and much better tracker than most other cartriges that I tried.
As a bonus for Koetsu, I find Koetsu cartridge in general to be one of the quietest if not the quietest cartridge and much better tracker than most other cartriges that I tried.