1 x 4gb is also slightly slower than 2 x 2gb. It depends on how long you are expecting to keep the laptop for and what you want to do with it in a few years time. If you are going to still be wanting it to later. I would probably suggest the 1 x 4gb as it won't be much slower and will be very easy to upgrade in the future.
there is absolutely no difference whatsoever, either one will have the same cock speed and make no difference, if anything it will be sightly faster
either one will have the same cock speed
Lols