Cold boot issues on asus p6t i7 920

Hello all! First post here...just started getting into more serious overclocking after just doing minor 10 - 20% increases on some old Athlons. Here's the setup:

Asus P6T SE Intel X58 Mobo
i7 920
Cooler Master V8 Heatsink
G SKILL Trident 6GB DDR3 2000 (PC3 16000) Triple Channel Memory (F3-16000CL9T-6GBTD)
Ultra LSP650 650w Power Supply
Sapphire Radeon 5850

Description of the problem:

On cold boots, my computer will turn on and sit there. No post, nothing on the screen, no sounds that I can decipher...just sits there. If I power it down again and try again, it starts up 95% of the time, but its hit or miss as to whether it will say my overclock failed and that I need to fix my bios settings. I always just hit save and exit as it saves my settings, and there's really nothing wrong with those settings in particular. I have no other problems...resets are fine, running benchmarks and putting the system under load is fine. Only if its been off for a bit of time does this occur.

Overclock settings:

The stepping I've been using has been 200 x 20 for 4 GHz. I had initially set the voltages manually myself, but after the odd spontaneous reboot during benchmarks, I decided to give ASUS's "Auto" configuration a shot and it pumped up the voltage a bit and the system is perfectly stable. I've increased the timings of my ram slightly (don't recall exact values) and the ram is OC'd to 1600MHz.

Now, my first conclusion is that its the Ultra PSU. I have heard poor things about this power supply but I bought it for my last system in a pinch after my old ones fan locked up and killed my video card. This problem (I think) has become more pronounced since I switched from an 8800GTS nvidia card to the new radeon 5850. It might have been my imagination...I haven't taken the time to unplug it and check how the system responds.

Obviously taking more time to investigate whether the graphics card is sucking up too much power on boot will be my next avenue, but is there anything that jumps out to anyone as to why this is occuring? I've bumped my core clock down from 200 to 190 (3.8GHz) and it seems to lessen the problem. Temperature should not be an issue as I reach CPU temps of 60 C under full load after 3 minutes at 4 GHz...and especially on cold boots I don't see how that could be an issue.

Any advice would be wonderful! Thanks!