Does that sound right?
I went from a TBred 2400+ @2040Mhz to a Mobile Barton 2400+ @2400Mhz and gained 700 3Dmarks

System is
NF7
Crucial pc3200 200fsb 2.5-3-3-11
Gf4 ti4200 64mb 290/580
xp pro

Tbred 2400:
http://service.futuremark.com/compare?2k1=7646597
Barton 2400:
http://service.futuremark.com/compare?2k1=7763089