Hey, Skip to the end for the straight up question.
I have some slightly defective Corsair Vengeance RAM. I can't get any of my and my friend's systems to post with it in dual channel mode, so I've been meaning to RMA it for... about 5 months. But, if it isn't affecting my gaming performance I really just don't give a damn. Passes memtest without errors in single channel mode (slot 1 and 2) and if I'm not loosing FPS while gaming (3770k 4.5GHz, MSI GTX680 lightning 1375MHz) I think I'll just leave it and purchase new RAM because it would only cost about 10$ more just to get a new set of 2x4GB RAM. And, the heatsinks are just redonculously huge and pointless, especially at 1866MHz. Maybe on boxing day there will be some sweet sales.
So, long story short, any performance hit when using two RAM modules in single channel mode?
To be honest, the 3770k is a decent CPU, and the i7 Platform does extremely well memory wise, You will take a hit running in single channel with the i7. I would personally wouldn't run single channel on any Intel for that matter just the way it handles memory, AMD on the other hand don't see much of a difference, But I know this i3 2.26ghz laptop is pretty slow with youtube in single channel, had to run single channel because 1 of the sticks went bad. but I mean Gaming wise you wont notice any diffence, but desktop wise yes you may notice.