Tobes - the Karat has very good bass response and exhibits bass/midbass texture very well but lacks a little in the bass slam department. This does not bother me too much mostly because of the type of music I listen too. So don't dwell on that too much.
The 103R is every bit as dynamic as the Karat and you gain some bass slam but you get a little less bass/midbass texture.
Also keep in mind set up with the two cartridges. With the 103R you can quickly get in the ball park and minor tweaks or changes seem not to phase it, but if you keep going you'll find its magic. The Karat is more sensitive to set up but more readily reveals changes.
Its tough to move up from a 103R because you have to go a few extra steps up the ladder for significant improvements.