Really excellent info guys, thanks! Just to clarify, I am not looking to up my avg speed on, say, a 30 mile ride from 17mph to 22-24mph as that is a very big jump and I also don't think that would be doable with stop signs, lights, etc. I am mostly trying to up my cruising speed on flats from 20mph to 22-24mph. But I am not that experienced and given the references to TT bikes/bars, maybe my expectations are not realistic? Then again, the 8% figure from DrIsotope makes me think that if I were riding a road bike on the same route, I'd avg 18mph and hit close to 22mph cruising on flats. I'm assuming the main difference would come from the wheels and aerodynamics vs weight and gearing.
I have worked on body position and have some jerseys and shorts coming, so am trying to hit most of the low hanging fruit and get better informed before spending any serious $ on either mods to the Surly or another bike.