😱 Well it seems standard Gainward (ie non-Golden Sample) use cheaper RAM which often struggles running at the standard 4200-128 and 4200-64 clock speeds. 98% of 4200-64 use 3.6ns which can easily cope with a 500mhz clock and can technicly achieve at least 550mhz (hence why it's so nice for o/c'ing). The GS do use the usual 3.6ns (hardly GS eh) but Gainward's std 4200-64 reportedly use 4.0ns which is only technicly certified up to 500mhz, hence EVGA (one of the other very few manus to skimp in this area) actually use a 444mhz clock on their 4200-64 in order to improve yield and maitain stability. JFYI AOpen are the other co known to cheap out on consumers in this way.
😉 Going for a GF3, Gainward and esp GS mean a lot, but for GF4 I'd look elsewhere.