Nexus 300w here and I have the flickering problem on Creative, Gainward, Reference etc. boards.
I have checked with two boards that appeared to use different voltage regulators (they looked very different) and they still have the exact same problems.
I think your description only fits because those are generally common components that you mention
sorta like if Windows XP had a bug with audio and people started reporting it it would look as if it perhaps was a Creative problem since creative has by far the most soundscards out there
and besides PNY eVGA etc. are all identical,
in fact all 5900 Ultra boards are identical right now, it has nothing to do with "cheap" manufacturers at all since they all buy their stuff from the same source and just put their stickers on it
in fact not even the non-Ultra differ much
check this out:
Can you guess which are 5900 and which are 5900 Ultra?
(as you can see the PCB itself is also identical except some odd few components and the color)
I think the only reason why this seems more common on non-Ultras is simple because they are clocked lower
because on the cards I've tried the problems become worse once you start overclocking