With regards to the 2 x2GB ram thing all I can think is maybe G.Skill use a selection of different IC's with there 6400 8000 & 8500 kits.

Based on pure speculation & a couple of bits of hear say maybe the G.Skill kits have the same sort of deal as OCZ which apparently can use 3 different makes of IC on there kits & its pot luck as to whether you get a kit that can clock or not

CN