I have the S&W Model 60 with a three-inch barrel, roughly the equivalent of the Ruger SP101. Fully loaded with 158-grain bullets, plus a reload and a speedloader, the Ruger is going to come in right at two pounds. That's less than a pound more than the Kahr CW9, empty.
A good belt and a good holster and you won't even notice the weight. Besides, you'll be glad for the extra weight and barrel length when it comes time to fire full-house .357 Magnum rounds the Kahr can't hope to match for muzzle energy.
The SP101 also offers versatility the Kahr can't match: load .38 Special, .38 Special+P, .357 Magnum, snake shot, self-defense loads, cheap range fodder that would probably choke the Kahr. Need more than five shots? Carry an HKS speedloader, it's almost as fast as changing a magazine.
I also own a Smith & Wesson Airweight. As much as I like my little pocket protector, it's a bit of a beast with hot loads.
For the purposes you describe, the Ruger is clearly the better choice. It's more versatile, more dependable and more powerful.