Jon, it doesnt just come down to weight, the 10 spokes are forged rather than cast, as a result they are as strong as cast aluminium wheels! although the rear wheel is so light when i first picked it up i nearly ended up launching it at the ceiling cos it was SO much lighter than i was expecting!
go to bikehps.com do a search on bst and you should get all the details. they have wieght comparisons rider feedback etc etc. not cheap but look to be the ultimate. or blackstonetek.com
Hmm, for the difference in weight I reckon you're better off with the forged mags, the 900 quid saving can go on some spare termis, you'll never know when you'll need them eh Tim