An offset overflow may create better flow in the tank, though it's probably easier to deal with a corner overflow underneath the tank, as in the plumbing.
Yes,
Oceanic seems to have a corner overflow which I have read mixed reviews about. Then I just recently read about the Jetstream tank which has two overflow systems. The link below will take you to the page http://www.marineland.com/products/c...on_jssuper.asp