Running the risk of saying something stupid, the speed of the 2 DDR3 modules will still be 10.6 Gb/s. It doesn't double speed just because you have 2, that math doesn't make sense.
Running dual channel increases performance but by how much it depends on a lot of factors, for example if you have old intel CPU's the answer would be almost nothing, for ryzen it would be by a lot.
Besides that timings and latency are very important in that comparison to.
To increase the information -
Dual channel lets the processor read and write from 2 sticks simultaneously. Thus increasing the performance throughput.
Yes the memory still runs the same speed, but the cpu has access to additional memory so there's less wait time while multi-tasking.
The reason why Single vs Dual channel in most games makes little difference is because the information is being written read, it's just being read after loaded. The GPU does almost all the rendering, so the effects of dual channel vs single are minimal differences.
Overclocking -
1 stick should always clock higher than running 2 sticks. 2 sticks faster than 4.
So you could maximize bandwidth but at single channel reduction which only effects certain programming.
And lastly, each DDR revision brings Bandwidth to the table. Bandwidth is king. Latency isn't everything. So each revision is a 50% increase in bandwidth. More information in and out at a higher frequency. And that's why we overclock!!!! Moar Poawer!!!!