What is your FSB as the your current settings? 2.5-4-4-11 @ 2.7 Volts is pretty crap. My XMS 3200 makes 2-2-3-5 no problem at 200Mhz FSB. Your timings don't sound right at all: the lowest timings I can find on the corsair website for your RAM are 2-3-3-6. From my calculations, if you're running your stock multiplier, and only upping your FSB you're running approx. 153 FSB, which is only 306mhz on your memory, and your mem is rated for 333,.. you should be able to drop them timings lower than stock. They are rated @ 2,3,3,6 @ 333mhz.. lower the speed, the faster the timings with the same stock voltage.
TGHI