I've built several deltas, and the tractor or "puller" configuration is definately the way to go.
You get not only better performance because of air over the elevons, ect. there is a benifit from the propwash over the airfoil at high angle of attack that makes these thing do unreal things-talk about impressive transition to hover.
Here's a couple of pictures of "Delta Burke" my 88" span, under 5 lb., .53 4 stroke 1900+ sq. inch area delta. Pure flying magic. Cost me under 20 bucks for the airframe, and it was built in less time than the average (easy) ARF.
Notice the drooped LE on the top picture, another "secret helper" for delta's
Jetts