How much usable meat do you get from an extra lean 1700 pound hereford steer?

That's a pretty large steer. Assuming that the carcass weight is 40% of the steer's live weight, you'd get a carcass weight of 680 lbs; with that, minus the weight from bones, you could get about 620 lbs of meat off of him. But it's hard to say without knowing the carcass weight.