Some K10, Barcelonas can go over 2.6 and all the way to 2.8 or even 3.0 GHz but most of them at least the ones that are going to come as corner chips on the wafer and not going to work at much higher speed than 2 GHz if not less.
This can explain why the first Barcelona we pictured back at Computex worked at 1.6 GHz only. The second trouble is that not all the chips from wafer works and we know that AMD is currently not happy with yields of the chips and will likely need another revision and it can pray that everything including clocks, leakage and speed is going to be fine. Otherwise it won't be pretty.
Most of the Barcelona or Opteron 2200 or at later date Phenom FX CPUs won't actually work at 2.5 or more, they will rather be clocked to modest speed of only 2.0 GHz or lower.
2 GHz is far from being enough to dethrone Core 2 Duo who even at 3.0 GHz sells for around $270 and as we said numerous times Quad core won't bring much versus Dual core. In case it does Intel already has two iterations of 3 GHz or close to 3 GHz (2.93) so the pressure is certainly on DAAMIT.