2x4GB RAM modules vx. 1x8GB for MBP?

Hey all, I recently got a base 15" MBP, love everything except the 4GB of RAM.....seriously uncool Apple. Anyways, I've been thinking about upgrading the RAM, and I'm not sure how to do this. 8GB would be a definite improvement, but I keep thinking that sometime down the line I might need 16GB. So if I do get 2x4GB and decide I want more, I'd end up spending a lot more on RAM than necessary, so I'm thinking of just going with 1x8GB for now and seeing how it goes, then adding another 8GB module if need be. Basically what I'm wondering is whether or not there's a difference in performance between the two, I read online that 2x4GB may be better due to dual channel memory but I just wanna be sure it still applies today as those posts were kinda old. Thanks in advance guys!