Out of curiosity - how did you get the 5850 to 391MH/s? What's the voltage and GPU frequencies? And what software do you use and how many watts does it use?
I've found mine to be quite stable when undervoltaged to 0.975-0.987 and GPU at 775-785MHz (which results in 305-308MH/s). On the good side - power usage is pretty decent - 675W with 5 of them mining.
Voltage : 1.199v
gpu : 950
mem : 350 (this is the "sweet spot" higher or lower will not give as much mh/s)
It's a sapphire and I use Trixx.
I just lowered it a bit at 381mh/s with a voltage of 1.162 and gpu at 920 to have less fan noise. I have instruments to measure the power usage but i'm at work so I don't care

This can be easily done at stock voltage mem@150 core@840. You only need to replace cooling paste with Arctic silver. Usage is about 180... And I have tested your settings. I think you need batter kill-a-watt. I can't make it run with the usage that you reported last time... It uses about 120W+. If I remember correct you reported 85W.
That won't give you 391mh/s at all more like 330.
I am wondering how you get the lower memory to work.... every time I try to decrease the memory in WINDOWS machines the AMD CCC app freaks out and puts the video cards to their default memory settings refusing to let me change it anymore. unless I use TRIXX but after using Trixx for awhile the AMD CCC App gets totally lost as to what the card is doing.
Like presently one machine that I was using Trixx on the AMD CCC app has no idea what the fan speed and temp of the card is anymore it doesnt display it. on another one it display them but has wrong value. another one I completely removed all amd drivers because the Trixx utility and the amd ccc app wouldnt control the card anymore...