Overclock CMD4GX3M2B1600C8?

I have 2 sets of CMD4GX3M2B1600C8 1600MHz 8/8/8/24 RAM running with a Phenom 965 and a Gigabyte 790XTA-UD4 motherboard.

So far I have tried dropping my RAM speed to 1333MHz and trying tighter latencies, but that made little difference to benchmarks. Am I likely to get better latencies at 1600MHz with this setup - or should I just leave it at stock?

You should be able to get tighter latencies at 1333 than at 1600. However, with 4 modules and the limits of any given memory and memory controller, you are only going to be able to go down to a certain point. And it can vary from CPU to CPU so you'll need to test it yourself. Running 4 up is going to limit you somewhat. Set your system up both ways and test it doing what you built it to do.