Almost certainly what OCUK have done for their profiles is have the fan settings incorrect, or fan settings you've got aren't working as well for a CPU with higher voltage/speed settings.
For 80C idle, frankly at idle at 4.2 or 1.8Ghz you should end up with similar speeds.
Depends on several things though, have OCUK disabled speedstep for their overclocked speeds, some mobo's won't go as high/stable when its dropping down speeds for speedtouch so its often disabled for the highest possible overclock/uber benching runs, for every day clocks/settings you can have a very good overclock and C&q/speedstep enabled with no issue.
So first guess anyway, that cooler, with those overclocks, 80C+ is madness even more so for idle, I would suggest the cpu fan is set to not turn on or up in speed below a certain load or something.
As for overclocking, you can as others suggested easily go from one stable system and overclock, to a new card, and its not as stable, so many people discount that when they hit new trouble with a graphics card.
Theres so many "my amd card is unstable, amd suck" threads with people who have gone from a 4850 or a 8800gtx to a 4870x2 and wondered why their system is no longer stable.
THough you didn't say what gpu you came from before hand you've gone to one of the most power hungry cards available ever so its not a huge shock that it could tip a just stable system over the edge.
Essentially I don't think you would have ANY trouble getting the 4.2Ghz back, and would probably put money on it being fan settings being simply too low for the given clock speed/voltage.
Assuming its a motherboard with bios control of fan speed, make sure all fans are set to full power for now and try the overclock again and check temps, then find a balance between noice and stability/overclock you want.
As for the "BSOD" message, the error indicated at the top has almost nothing to do with memory. Almost any unstable system will BSOD with driver issues at some stage, and almost every time windows decides its a driver that caused the crash it will give that error. Yes it CAN be caused by memory, or a 100 other things, most instabilitys show up as that error and manifest in drivers failing and gpu drivers fail more frequently than others, purely because they are bigger, more complex and more used than basically any other driver.
