Bottom bracket quality

[Psycolist]

I've spent about 2 hours tonight searching the net for anything that will tell me about the different quality offered in the range of Shimano bottom brackets. I'm not the greatest at computer ANYTHING, but have been unable to unearth anything regarding the UN25 UN26 UN55 UN54 or any other series of square taper BB's, other than the prices they are offered at. Can anyone point me in the right direction please ?

 

[RecordAceFromNew]

For decent quality JIS I would go for the UN5X series. Unfortunately Shimano stopped making higher quality (well lighter) ones some years back, so the next step up costs 10x more and is hard to justify imho.