I have tried them all ,my (BFG 5900XT) has been flashed
almost 50x ,As far as I am concerned A 5900 (what you are calling it)
Is a 5900NU ,and they have a better ram than an xt .
My best flashes with lower temps,and higher clocks ! has been modded
(under clocked 5950U ) bios with way loser timings (MSI or BFG)
What it does for the 5900XT is give you that lower operating
temp.and sets the bar lower as a starting point to go from there.
I run my card for every day at Core=490 & Memory=890.
but i get the lower temps ,because of the 5950U bio.