I think 3GHz (320x9.5 = 3040MHz) from a 1.9GHz budget part might be pushing it unless you have a very good chip there, only very few reports of that
CPU hitting much over 2.8GHz, the 280MHz HTT with the stock multiplier of 9.5 making for the 2660MHz you are currently getting is not exactly a bad overclock for that
CPU.
With better cooling and increased volatges you might get a touch higher, however as the memory controller is on-die this means that even if a memory divider is used a high HTT speed can be hard to achieve.