I don't know that doubling the size of the skimmer for the system is the way to go. Some of the higher end skimmers on the market actually skimm too much from a system I have found. Maybe if you had a fish only system you could go w/ a oversized skimmer. So basically alot of the higher end European skimmers don't need to be oversized and you are wasting money in the end. A appropiately sized skimme will give much more consistent skimming.
What makes a godd skimmer???? R&D and a company that is willing to stand behind its' product and does'nt use the customers as their R&D dept. When we pay as much as we do for these things we should not have pumps that won't start,micro bubbles from the drain,overflowing, etc. I would say buy from a company that has been in the game for awhile and has a reputation for helping customers w/ problems. Customer service is huge IMO.
As far as design goes. I would look for a good pump, Aquabee,Tunze and Eheim are good solid choices. Companies that have been doing it for awhile and companies that are using these pumps are generally very easy to deal w/ when there may be a issue. Where the skimmer manufacturer comes into play is getting a appropiately sized body, riser tube/neck diameter and height. I like wedge pipes becouse they are simple and no fuss. Tunze has a nice drain pipe design as well. Air flow adjustment is key on some skimmers and a nice silencer to cut the air suction noise.
A good skimmer should be able to run wet as well as dry. This all comes down to the neck dia./ height, air input and having the flexiblity to control water level in the skimmer (drain) and air input. On a good skimmer you should bee able to run air wide open and control skimmate (wet/dry) w/ the drain valve.
Again, if you spend a bunch of money on a nice skimmer you better be getting fantastic customer service.......not the run around!! What good is the best skimmer going to do for your system if you can't get replacement parts or unanswered EMs' and so forth??
Just my .02
Chad