I think with the B7 you have to make sure there's plenty of wood behind the bridge --it's a pretty long trem. The bigsby site has measurement's I think. Other than that, both look cool in their own way. I think the downward pressure is the same, since they both use tension bars. I think the B7 is more common on archtops, and the B5 more for flattops.
There are other bridge options, sure. You could go with the Bigsby rocker bridge or the compensated wraparound (doesn't matter where the strings come from), although, true they're both TOM style.
But if you look at this guitar:
I modified the bridge for the Bigsby by carving slots for the strings. Worked great (I eventually took off the Bigsby when I modded the guitar again, then sold the Bigsby...kind of wish I hadn't now...I'll have to get a new one).
You could do exactly the same with a hardtail bridge, maybe with a three-barrel type.
Didn't the strings bind up in the slots when the Bigsby was used? Seems like a roller bridge or maybe graphite saddles would help the Bigsby work smoother? Again, I don't have any experience with one, but I would prefer to not have to use a tunematic style bridge and angle the neck pocket.