I specified because the Bosch isn't the only pump available.
snowtrac is right that sticking with another 3116 is easiest, but, the 6CTA engines seem to be cheaper (absorbing the costs of having the charge lines, exhaust, etc all fabbed again). They also seem to be easier to work on although I suppose that's a matter for debate. The thing that I keep looking at though is the 5-6MPG of the truck. I put anywhere from 3k-6k worth of fuel through it a year. Even a 25% improvement in fuel economy is going to mean big bucks down the road.
I know physics is physics, but plenty of others have bigger, heavier things that are getting better mpg.