asian made bridges are usually 51-52mm
I think gibson bridges sold separetely aren't notched, unless they came in a guitar, and the spacing will depend on stock pickups
as said, the Gibson "XXXT" models are 52mm
most fixed bridge guitars I had, aligned much closer to 53mm pickups than 50mm
and I've had problems a couple times with les paul copies that had misplaced bridges... a bridge that's 1mm out of place to one side can mess everything up
the higher E strings in my jap hurricane lp copy (wide spaced stock gotoh bridge) loses some sustain with 50mm pickups, unless I bend the legs a bit to get the pickup to the right, or align the strings over the saddles
the stock pickups were also 50mm and the E string was almost out of the bridge pickup right edge, so it DID lose volume, sustain and tone
doesn't make any noticeable difference when you have a 53mm pickup with a 50mm bridge, though
as most of the guitars in the market have wide spaced bridges, I tend to order 53mm
that's actually the first time I only have 50mm pickups (riff raff, black dog, mule, warpig, and VHII's by next week), but some were used,so I didn't have much of a choice :D