I'd say go for the KR, but as I have a Pentax I would say that.
However, you have handled one and like it, and the backwards compatibility and in-camera IS are also big plus points.
Old manual focus Pentax K mount lenses can be picked up fairly cheaply.
The only concern I've read about the compatibility of old lenses is the following -
PENTAX: ALL Pentax K-mount lenses will work on ALL Pentax bayonet bodies, including autofocus and digital. For "Program" operation with some models, you will need a Series "A" or later lens. A note of caution, though: there was a KA mount for Pentax, and also a KR mount for Ricoh program cameras. Both of these have the same K bayonet, but the location of electrical contacts is different between them so that they are not cross-compatible for program functions. ALSO, AND MORE IMPORTANT, it is possible for some KR lenses to jam on some models of Pentax cameras, and be impossible to remove or cause damage to the camera or lens. In particular, it is not wise to attempt to mount a KR lens in an Autofocus or Digital model of Pentax. There may be other incompatibilities as well, so proceed with caution whenever cross-mounting Pentax and Ricoh lenses and bodies.
- but this looks like something that is easily avoided.
I use a few old lenses with my Pentax with no problem and must admit I quite like the idea that I have image stabilisation with a lens I bought in about 1980.
Dave