Yes I do have a set of md lenses I love using. I'm mainly looking at the xk for a more rugged body to attach those lenses to. As I can at time put a beating on the cameras I take to events. As my x700 has a problem with the film speed selection wheel due to taking a tumble. I'm wondering if the xk will hold up better then the x700 in that regards.
Don't need another system in my life. With already having Pentax k, m42 and md.
The XK has quite a range of useful features. If the amount of lighting in the venues you shoot is poor, then I would recommend that you use the AE-S viewfinder as it has silicon cels which are more sensitive as opposed to the CDS cels in the AE finder.
Unfortunately, the waist level finder of the XK is not metered. However, since you do have Pentax K and M42 lenses, then perhaps you should consider the Pentax LX instead as it's waist level finder is metered. In fact, it has the most comprehensive selection of finders among these types of bodies and they are all metered. They range from best eye-relief to the largest magnification and have diopter adjustments as shown in the picture below. All very bright.
Among other things, the LX is the most weatherproofed, has wide range of shutter speeds available if batteries die - including self timer, TTL flash with traditional hotshoe, motor drive options and is the smallest and lightest of the bunch. Practically the same size as the non-interchangeable prism bodies.