Engineer Dave:
I was confronted with a similar situation several years ago when changing jobs. And, I was looking at cost-of-living studies and such. However, I was also looking at moving, which I don't know if you are. When I threw in taxes (state and local), housing, benefits, retirement plan, relocation package, etc. as something else to look at, one job (even though on the surface more attractive) was immediately dismissed. A high profile position and mid-range salary couldn't compete with the other offers.
Additionally, a second company was dismissed when I started reading about their company from various websites (including the Yahoo business boards). I found out they were being sued on several fronts regarding labor. Six months after turning the offer down, they lost the lawsuit and half of the management team was out the door (and it could have been me).
What it came down to was 2 companies that everything seemed to be on the up and up, the only difference being salary. (Benefits were about equal.) When I compared taxes though, the lower paying job was in a state without local or state income taxes. So, the difference in salary was alleviated. So, the only 2 remaining offers I had were about equal. Personally, I picked the lower offer company, told them I had another offer for more money and an extra week's vacation, and waited on the "No". The good news, they didn't come back with a "No" but with a matching offer (without me prompting them for an exact increase).
I guess what I'm saying is to look at much more than just a salary difference. And, when you are sure of your facts and figures, and CONFIDENT in yourself, state your case clearly and consisely, don't beat around the bush.
Good luck with the new job! (Whichever one it turns out to be.)
~NiM