For the OP
I agree with Marc's comments.
I would probably consider keeping the second DS that you own, specifically for support of TTL flash. Since you use a lot of M42 lenses this to me would seem to be an important issue.
Aside from that point, any new camera with SR offers a significant benefit, and the K-X would be a huge improvement in that regard.
With respect to metering I have posted the performance of *istD, K10D (stock screen) K10D (using *istD screen) K10D (using Jinfinance split image) and K7D with stock screen, all done using an SMC-Pentax 50mmF1.4 lens several times.
I truely wish other forum members would take me up on the request to perform a series of shots and either e-mail them to me or post JPEGs of the center 10% of the shot, when using green button against a uniformly lit block wall or paved surface, so I can add the performance of all other cameras and focusing screen variations. It would be a great benefit to all those who have questions about manual lenses and metering performance
I have attached my results again for reference.