SM7 vs SM7b

I've never heard the original 7 but Bruce Swedien has implied it sounds better than the revisions in interviews.
As far as Unidyne 3 relation between the 57 and 7, it's sort of like saying a new beetle and a 911 are the same car b/c they're both based on the original beetle isn't it?
 
Yeah if anything people "think" the 7 sounds better. We have a 7 at the big studio I work at, and a 7B at the other. They're pretty much the same, just the B has the better mounting. Just buy the one in the best condition. They'll both be workhorses.

And yea the capsule is BASED on the the unidyne iii design, as are the 57 and the 58. But everything else about it is different. They explain it a bit here http://blog.shure.com/shure-notes/sm57-on-steroids-the-shure-sm7-b-story/ if anyone cares.

The SM7's capsule has been changed from the standard unidyne to alter the low end response, and the body was made much larger to tailor the low end response as well. It sounds different for sure from the 57, but has a kind of similar sonic character.
It also has a completely different grill, mounting system, and uses like 4 times more material. That's why it's more $$$ than the 57/58
 
On vocals I can sort of hear how you might thick the 57 and SM7B sound similar but on every source (guitars, snares etc) they are wildly different animals.