what is holding this back from oc'ing? heat isnt a prob

Hi guys,
I'm currently on a prescott 550 (LGA775) P4 3.4ghz with a Corsair 512x2 DDR2 PC-5400 memory (4-4-4-12) , GigaByte 8I915P Duo -A Mobo
right now I'm using the 14x multiplyer instead of 17x.. i'm using the 14x in order to make use out of the ram at a 3:4 ratio (fsb:ram)
fsb right now is 251 (x14) = 3.51ghz
and the memory is 335mhz (x2) at SPD timings (4-4-4-12)

however, my current vcore is 1.328v and my vdimm is now +0.1v.. dont ask me why but it only is stable when its +0.1v :s

I can go for 4ghz but not with the 14x multiplyer as my system is never stable at this point (dont ask me why)
but when using the 17x multiplyer i can hit 4ghz with the 3:4 ratio,, but the downside is that i still wont be making full performance out of my memory..
I tried so many different combinations of lowering timings/changing divider and those things.. but nothing really is stable except my current setup.
heat is never a problem for me right now.. even when going 4ghz using the 14x multiplyer

I'm current using 2 HDDs (1xSATA 1xATA133), a DVD-RW and another CD-Rom, 3 case fans, with some nonbranded 450w psu.. and below is the screenshot for the psu specifications

my main concern is, is it the psu that is holding me back from pushing my overclock further and causing the system to restart itself and not boot?
the reason I thought its my psu is because of its low amps on the 12v rail compared to the other people who got their systems pushed hard..
and btw, the PCI-e/AGP frequency is locked

thanks alot, any help is appreciated

ic,
my current temps on the 3.51ghz with the "smart fan" disabled (so, running stock fan at full speed of 2600rpm) is 30 idle and 50 load.. but thats just because i'm currently having my case opened.. however.. when closed + proper air flow.. its 35c/52c on the 3.51ghz..

if the problem is from the psu .. then what would you guys suggest something good for oc'ing? something thats not too expensive but is still considered good for ocing and stability issues..