100mm M42 Lenses

The meyer is a lot easier to focus than the Pentax but that shouldn't be a problem with what you will be doing. You can play with the aperture using the Meyer and see in real time what is happening. You need to use the on off switch to check depth of field with a Pentax. Being intended for macro, the Pentax is a bit clinically perfect whereas the Meyer has character. The Meyer has about 15 blades that produce a perfect circle vs the Pentax's 6 and they open to f2.8 vs f4. I note you do a lot of car chasing and suchlike that might entail fast changes of aperture - the Meyer doesn't like its iris being whipped from one end to the other and you stand a high risk of damaging it. Those blades are delicate by comparison to the steel plates in a Pentax. You have to treat all Meyers with care.

I love my Meyer lenses and admit to being completely biassed! You could also try the Takumar and/or Soligor 105mm too.