Stagger reduces induced drag in biplanes, but its effect is roughly a third as much as that of gap. Increasing stagger by 0.3 of chord will reduced induced drag by about the same degree as increasing gap by 0.1 chord, within the normal range of stagger. Going to positive stagger of 50% of the mean chord will increase maximum lift by about 5%, according to old wind tunnel tests. The same amount of negative stagger, like on the Beech 17, will slightly improve lift/drag ratio, and make the stall more abrupt, compared to an unstaggered layout.

Unusually high stagger will tend to require increased horizontal tail area and elevator area to fight the tendency of the wing combination to resist pitch, much like a tandem layout such as the Rutan Quickie, which has no horizontal tail.

Most of my own bipe designs use a gap of about 1.25 times the mean chord. This would result in an impractically large gap at an aspect ratio of 6. I like to use tapered wings, with the gap at the root about equal to the chord, which is easy to accomodate and gives good aerobatic line-holding. Layout is generally similar to the little indoor bipe in website
http://ramicrolite.com

My previous post has a bad typo - induced drag is, of course, inversely proportional to the square of the span, not directly proportional.