Recirculating models tend to be more efficient, you can keep the water in the skimmer longer, Not sure if you've ever looked into it, but Recirc skimmers can either be fed by your overflow, or a seperate pump, such as a maxi-jet... then of course the Recirc pump does all the work inside the skimmer......
As for out of sump, I was always too chicken to try it,,, because of floods,, not sure how many people had floods with them, but I like to be safe...
Have you checked out Orca Systems custom skimmers? (protein-skimmer.com) I have one on my 120, in-sump, recirculating.... Couldn't be happier!! Awesome craftsmanship! That and the price was right!
If you need more info on the skimmer, check out my homepage, under the 120g section.....