Just speccing a P67 system.
Is it still the case that 2x4Gb modules will be better than 4x2Gb modules?
For overclocking and future upgradability yes.
(No, that's not a word, but meh)
Why is 2x4 better than 4x2?
I bought my system with 2x4, but will most likely grab another 2x2 or perhaps even 2x4 set later on, taking me to either 8 or 12GB respectively, as my need for VMs increases.