You can't get a 2500+ to 3.0 unless you overvolt it like mad and put phase-chage cooling on it. If it's a desktop 2500+ with a good stepping, 2.3 is realistic with good air cooling, 2.5 with watercooling.
Anywho, I have an Athlon XP 2400+ overclocked to 2166 mhz.