There are no distinct differences from 8gb(2x4gb) and 8gb(4x2gb) ram aside from the 2x4gb will leave you with open slots for upgrading in the future.
For the i7 950 though, I would suggest you get a triple channel kit which would be 3x2gb, or 3x4gb. The 6gb(3x2gb) should be more than enough. You would only need 12gb(3x4gb) if you do video rendering/photo editing.