whats not convincing about the K-7?! if you are using a 40D, and even considering the K-7 you have to know its 1: far better suited for manual glass and 2: a far better camera than the 40D in virtually every way. if you are seriously considering manual glass, Takumars especially (be careful, you are heading into addictive and possibly very expensive waters) the k-7 will be the absolute best digital body you can mount those Takumars to. I say this, get started collecting your Takumars. (I personally recommend a 55mm 1.8) wait for the price on the K-7 to come down a bit, sell the 40D, get a K-7 and never look back. I can assure you and im sure others will agree that a pentax body (especially the K-7) is just a better choice for Takumar lenses.
and welcome to the forums.