Memory "Kits" and adding memory later. And two 2GBx2 kits -vs- one 2GBx4 kit.

[Mark]

I'm looking to build using GA-P55-UD6 and an i7-860.

I was thinking I'd start with 8GB of DDR3 now, and add more later if I needed it.

However, I'm confused about the implications of these memory "kits" being offered by memory manufacturers (and newegg, for example).

I understand that we want matched pairs of memory, but what if I bought two kits of 2GB x 2 and put then in one motherboard.  Would that be so different from buying a kit of 2GB x 4?

I can find 2GB x 2 kits running with a CAS latency of 6, but the lowest I can find for 2GB x 4 kits is 7.

Thanks!

[Beekeeper]

it's always more safe to buy kit of 4 pcs
CAS is increased to avoid common problems when 4 DIMMs working