The Karat is a fast, detailed and dynamic cartridge that to my ears is really pretty neutral across the frequency range. I would definitely not put it in the lush and warm sounding category. No problems with tracking and all the soundstaging and imaging tricks are there too. It leaves me wondering what improvement the XX2 would/could possibly make!?
The only Sumiko cart I have experience with is a Blue Point Special (latest version). It was a good cartridge for the money which is why I considered the Blackbird. The BPS got a little edgy when the volume went up and seemed to lose its hold on the music when things got complex.
Good luck.