Won't benefit from higher clocked ram. It'll just run at 1066.
If you are planning to re-use those RAM later on, it might be worth it to get a DDR3L (1.35V low voltage for IvyBridge+ laptops) RAM. Otherwise, just get the cheapest & reputable brand RAM you can get.
I don't think lower CL really helps.
It's a business system, RAM speed and CL won't have much of an effect on it. The only time one should really try to get the top speeds out of RAM is in systems that are being used for overclocking and basically "show off" systems to try to get that extra few frames in a game to top a friend.
For standard systems like your DELL, you will have to run a benchmark to notice any difference, you're looking at a few % points at most of a speed increase. Fancy fast RAM will seem identical to you as standard RAM.