I see. Well, the applications in question are quite demanding, as typical of graphic games. E.g., TES-4 Oblivion tweaked to allow addressing more than 2 Gb memory.
Seeing as all hardware settings are intervowen, I guess I'll go for the higher cl & bigger size; otherwise, with both modules running at the same settings, there'll be either over- or underclocking of latency & voltage settings on one of them...
Unless there is some BIOS option to process the modules in a different way, separately (is that theoretically possible?), or, maybe, some utility for that?