Well, having your head at wheel level is fine for aerodynamics, riding around a closed course, but it's darn right scary looking at car wheels, much less semi truck tires, on the road. It's nice to be able to see the drivers eyes at an intersection, to see if the woman on the cell phone actually sees you. Coroplast is easy to work with, so you can build a fairing in a day or two. Getting a mold right takes months. It's good to build a mule and skin it with coroplast to get things worked out. I can average 20 in my coroliner fairly easily. In 2009, I averaged 32 mph for an hour at Northbrook and 22 mph for 12 hours at Calvin's 12 hour challenge in Ohio, but that was with the top on in race mode. I also sprinted to 40 mph on a level bike trail.. Sitting in a more upright posture is much easier to balance and climb. Having the pedals too high above the seat leads to fatigue in your legs, like holding a weight over your head where your arms start aching, the blood flow is less, so it gets really slow going up hills.. I usually place the bottom bracket 3 inches above the seat and seat back around 50 to 45 degrees. I prefer long wheel base, they ride better, no chain or heel interference with the front tire or axle, but are long, heavier, and don't handle as well. My touring street bike (pictured above) currently has the seat 12 inches off the ground. You should check out the WISIL site.
http://www.wisil.recumbents.com/home/