XP thoughobred is the core of XP processors that predecessed the Barton. Barton core is on all the newer XP chips and Barton is the better one. But more expensive.
the bartons run at either 333Mhz or 400Mhz effective FSB. i know for sure at least 1 version of xp2500 barton is at 333Mhz FSB and the xp3000 has both a 333Mhz and 400Mhz FSB version. well actually newegg lists it as: