overclocking problems

hi guys, my dream system i was supposed to get yesterday went to pot as scan had sweet FA in stock.. and i mean it.. hardly anything worth buying, so im having to wait till after christmas and im going to shop around wrather than using scan.

i couldnt walk away empty handed though so i got an abit GD8 for my p4 775 - 3.4ghz, to replace my gigabyte.

so here is what is running..

p4 550 (3.4ghz)
512mb corsair TwinX 4000 (500mhz)
pci-e xfx 6600gt

and that ****ty new abit mobo.

when i originally got built this with the gigabyte motherboard (earlier this year) i had absolutly no problems hitting 4ghz on a decent hsf, but now, running a dual radiator watercooler system, i struggle to get above 3.65ghz

i havnt overclocked for a while, so im expecting im totally missing somthing, oblivious to an obvious fact!

the downside is that **** **** motherboard here doesnt up' the voltage by .25 value's at a time, but by 5%, 10%, 15% and 20% selections.. (5% more than stock vcore)

the fsb, n/b and ddr however u can do at .5 value's

has anyone got an idea what the problem could be??
*edit* and before anyone says 'yeah ur using an intel' believe me.. i know
cheers guys

Erm, can I ask why you bought something that you didn't really want?

Also, did you check Scan's website before going, as this would have informed you of the (out of) stock situations.