RAL is a bit more involved then pre-rendering fps. And, has a very noticeable impact that I don't see with FQS changes. For AMD FQS of 0 is none existent.
In a nutshell RAL prevent the CPU from being ahead of the GPU.
A benefit using RAL when FPS is capped? I don't get the impression that capping frame rates is of particular importance when it comes to RAL. Remember this is about reducing Input/Peripheral latency not
pixel latency (g2g, etc).
Try it with Freesync enabled and disabled. You shouldn't notice any difference.
I've read that in certain FPS ranges they noticed the best benefit using it. But in those cases, I assume, are more GPU then CPU limited. IE: running at 1440p instead of 1080p for example.