Thanks for posting how you've been doing this - it's always interesting to read about other's techniques. Only 20 minutes south of Long Beach - that's not all THAT far. Might be a good spot to practice for our January trip to the desert and the Salton Sea. I'll have to work on it.
The K10 does have the capability of using ultrasonic motor lenses, but I think I read somewhere there was a hang-up with copyright/patents that was going to delay anyone coming out with a lens in the Pentax mount. Hopefully it will be solved quickly, I'll definitely check them out when they are released. At the moment the AF won't matter since my 300 lens is manual focus.
One of the options you can set on the K10 is how it comes up with exposure. You can set it to weigh shutter speed higher than aperture or aperture over shutter speed. I like using the P mode for just general walking around, but I've noticed with the K100 that sometimes it would "choose" a slower shutter speed and smaller aperture. Normally that would be fine, but not if I'm using the A*300, where 1/125 is slower than I want. With the K10 set to emphasize shutter speed, it'll stay at a larger aperture and choose a faster shutter speed - more to my liking with a long lens. With the K10 and P mode, I can always adjust things if I decide I want a bigger DOF for a particular picture.