Time is money.
I don't believe a 292 will perform time wise as fast as a 454. Look at the comparative torque specs of the two motors and consider how the truck will accelerate with one versus the other.
Okay I'll admit to being a fan of big torquey motors. A 292 may be a very hard working motor, but I'll be the last to believe it will perform hauling loads with a big block.
Mileage might be another matter, but I agree with Scott, in limited use its not likely a difference in mileage will make much difference.
