I never rode the EX250 with the Avons. They were worn out, so I replaced them first thing. But even with the tread practically gone in the middle on the rear the Avon was still several pounds heavier than the same size Dunlop.
In
Index of /graphics
there are scans of a series of articles from Cycle Guide (files named "ltwtweapon") in which a sub-200 pound 250cc Yamaha MXer was built up. The writer weighed
every component that went into the bike, which quickly made it very clear that you can't build something really light without comparing the weights on all the bits. Tires, tubes, handlebars, levers, sprockets, etc etc etc all varied a lot for pieces from different manufacturers.
Once you get started weighing things it is easy to find you've just got to have a nice lab-grade scale to let you chase tenths of a gram.
cheers,
Michael