RE: best bang for the buck?
Well damn, you're already two steps in on my list. Geno's right, it's up to a coin toss at this point. But if you plan on doing the converter, i'd do it before the headers. That's simply because the headers MAY make it more difficult (or impossible) to remove and install the trans, which is necessary when installing a torque converter. From what i've heard here, you can still wiggle the trans out between the headers, but there is a possibility (depending on the headers) that one side will have to come off to remove the trans. That's only a possible problem with long tubes though, with midlengths you won't have a problem.
Personally, i'm doing headers and the converter at the same time, sometime this winter.