I've had 2 sticks of ram with Nanya chips, one Infeneon the other I don't remember. Both work(ed) great for me, but I don't overclock that often(just for kicks once in awhile).
I'm not sure about this info: I believe that Nanya is a subsidiary of VIA. I also believe that Nanya produced(in marketable quantities) the first CAS 2 DDR ram.
Flatbroke: Have you tried lowering your CAS to 2.5 or 3.0?