I've got the Sport Utility bars on my Compass, and have noticed no significant drop in mileage or increase in noise.. The increase in frontal and wetted area from the bars themselves (compared to the vehicle without) should have a fairly minimal drag impact.. save for, perhaps, some vortex effects from the mounts they shouldn't produce _that_ much drag. (Unless you're planning on taking your compass supersonic any time soon.)
Slap a Thule Atlantis 1600 roof box up there, and then you're talking nontrivial drag effects..
Hmm, wondering if I could build a wind tunnel model of my Jeep now.. :P
"It's always suicide-mission-this and save-the-planet-that. No one ever stops by just to say 'Hi' anymore.." - Jack O'Neill
~No Longer Breathlessly anticipating my '08 Rallye, now just enjoying the [Expletive Deleted] out of it.~