A mobile 2600+ is rated up to 2ghz, not 1863mhz (that's the 2500+)
2.4ghz at 1.8v seems a tad high, but if like previously mentioned, your mobo undervolts, then you're right about where you should be. Most of my CPUs could do 2.5-2.6ghz air cooled (IQYHA's), but the voltage required for those speeds would have killed the chips pretty quick...I'd rather be sitting at 2.4ghz with 1.65-1.7v or so...
2.4ghz is nothing to sneeze at though