http://www.aquariumcontrollers.com/files/skimmers.html
This is a pretty old chart, but fairly accurate from what I've seen. My biggest thing for skimmers isn't really what they pull, as long as it's consistent. They need to skim enough to keep the nutrients down obviously, but a skimmer that you need to mess with constantly will be pretty much useless in the long run.
For example. the neck on the coralife skimmer is small, so trying to balance your skimmate from a wet to dry skimmate is a VERY fine adjustment, this also changes with air pressure and water level, so if you have your sump water move 1/8", you go from a wet skim to no skim. It was VERY frustrating, half the time I'd not be skimming, and the other half I'd be dumping all my skimmate back into the tank. After trying a few others, I now have an ATI skimmer with a nice large neck, I have a very consistant skim, and never have to worry about it. I've set it to a fairly dry skim, and it does this for weeks/months without me touching it.(unless a crab goes down the overflow... those guys love my skimmer intake)
Anyways, whatever you end up thinking of getting ask on this forum for past experiance, there's some good low cost skimmers that preform very well, and other high cost ones that are not worth the plastic they're made from. Some people like Skimmer King have owned pretty much everything, so know far far too much about skimmers and have very good advice on what to get.