I'd go the same speed I go now... 55-75 pending the street. I feel comfortable at that speed and really dont feel much of a need to go much faster. Also I have no problem letting those who wanna go faster just pass me and I have no issue passing those who dont want to go my speed.
My truck does decent on gas as it is, I bet if I floored it anymore my mileage would go down significantly, especially considering most all of my driving is stop/go country miles.