If I can remember (it's been a while) the biggest difference is that the longer Prestige butting is better suited to take the long term heat that is associated with brazing. With Tig, it's over pretty quickly and dissipates quickly and doesn't travel as far down the tube. Prestige is heat treated, nivacrom is not. Tange has introduce new Prestige in '06.

I've stopped making frames many moons ago and all the info I knew is now foggy. I hope I'm giving out the right info.

I do remember Ritchey had Tange make them a signature Ritchey tubing line called "Logic". This was prestige that was very thin and made cyclo-cross frames from it called Sub-22's. Very light for the time but went soft after a year or two of hard riding and not recommended for heavy riders, a lot of them snapped.

The trick is to find the same tubing weight but also able to handle the long term pounding/rider weight/dent Resistance and nice ride quaility that hopefully the new tubes can offer.

Cheers