Any drawbacks to mixing single-channel and dual-channel for RAM?

Hi, I currently have 2x2GB Corsair DDR3 1333MHz RAM which I had bought around 3 years ago. I am currently thinking of upgrading to 8GB. However, my vendor tells me that 2GB sticks are no longer available for Corsair and that I have to either get a 4GB or 8GB stick.

My current 2x2GB runs in dual-channel mode. If I buy an additional 4GB stick, it will run in single-channel. I use the desktop mainly for gaming purposes. So, I just need to know if mixing 2 modes will cause any problems?

Shouldn't cause any problems assuming it is otherwise compatible.

The difference between single and dual channel is minimal for most usage scenarios. If the RAM you have now magically went to single channel 5 minutes from now, you likely wouldn't notice.

You could discard the 2 x 2 you have now and replace with 2 x 4 and get dual channel, but nothing at all wrong with instead spending that money on cigareets, whiskey, and wild, wild women. At least you'd have something to show for it.