The difference is the memory. You have better memory than I do and I think that is why you can acheive a better OC. I've been battling with this memory problem for quite some time. I think your DDR 520 much better allows for higher OCing because as you increase the OC your memory doesn't overclock as much. My DDR400 starts overclocking the second I increase anything so I had to drop it down to 133. We've got a pretty similar system with the exception of the memory. It's nice to see that someone else with the Ultra PSU can acheive a high OC like that. I keep hearing from people that the Ultra PSU is the reason why I can't OC any farther but I think you just proved them all wrong.
Some advice, when you make the blow hole, make sure you have enough room between your PSU and your drives and keep in mind the big fat 20 pin line that comes out on the back side of the Ultra PSU. I was afraid to put a blow hole in mine because of that. I didn't think I could fit a fan inside there because of that 20pin line. Not to mention that all of those Ultra lines are stiff as heck. They are just really hard to get around. Maybe you could put the fan on top of the computer instead of inside. I dunno, just a thought.