Thoughts:
I get 15.5 MPG in the summer (750+ miles per tank) and 14.5 in the winter. Most of my driving is a 24 mile commute. The F450 spins at 2000 RPMs at 65, 2400 will be 78. If you drive a lot above 75 or so, I can see the merits of a taller gear; otherwise, the 4.30 works great.
I emailed my build sheet to Sarat Ford...they wouldn't match the offer I got from Balise Ford (the next town over). I have heard good things about Sarat Fords customer service though FWIW.
Coming from a 2002 F250 7.3 so really looking forward to the new ride.

I got 2 PMs on all this chatter, and yes, since I own both '17 model trucks, I can clear this up some more. Yes, Ford does make 2 similar trucks but the main advantages you or I will see are this:
F450 (with 4.30)
-Sharper turning Radius, which is nice to have! (but for me, 99.999% of my driving I wouldn't probably use. It could be handy however!)
-Larger brake surface (rotors). Now this for me would be huge! Really would like this.
-Name badge. Some people relate a higher number to a higher value. I do not however.
F350 (with 3.55)
-Tad better Mileage, especially and most notable on the high speed slab type runs.
And that's about it in a nutshell. I begged my dealer to order me in a F450 (for my personal tow vehicle) with 3.55's. He said no way, no how, it can't be done, and doing it after is a messy job along with warranty issues that he didn't want to deal with. You dealer could be different however?
And also per another PM; What do I think the difference is on the highway (slab) between my two trucks? Best analogy I can give you that the 3.55 is much like my F450 but with an added overdrive. So 6th gear in my F450 is like my 5th gear in the F350. Some will say this is no big deal, and it isn't to the engine itself, and after logging a couple hundred mile slab trip with the F450, you actually get use to the additional RPM's and not even think the engine is spinning faster. It's really a smooth a quiet engine, moreso than even my past Duramax's.
So more advantages to the F450 for sure!... and one's I really like, but for me and my mostly Interstate driving, I had to go to the F350 so I could get that lower gearing. Your case could and probably is all different than mine. Heck I've had people say to me "with a rig like yours, why worry about mileage!" hehe. Well, on cross Country trips, it surely adds up!
And the asked "what mileage difference is there?". Well, they both aren't equipped quite the exact same, and my F450 has an aluminum utility style flat bed on it. I can say hauling 4 tons on it of lets say water softening salt (or wood pellets etc that we sell), it gets worse mileage on the super slab than my F350 does towing my 21K lbs toy hauler (camper). It's a very slight difference here, but with that weight indifference? Yeah, the 3.55's are just better (economically speaking) for doing the slab runs. Now take that same 4 ton F450 haul through rural roads and neighborhoods, the gap would close considerably.
Bottom line here, if you don't do a ton of slab, the F450 would be my recommendation. Especially if you have a fleet fuel card or something where you're not actually paying for the (now and uprising) costs of diesel fuel. Added to this diesel thought, If you don't have the need, heck I'm all for even a good gas engine too, I said it before in another thread, get what you want or need!
My 06 had a 3.73 and the truck did ok, It would have bee nice to have the 4.10s on some of the longer steeper grades we pull every now and then. Again my situation is was different than most as I don't DD my dually. Honestly for me if I could have found a nice clean used, or new 15-16 F350 with the tow boss package that's ideally what I would have gone after.
Thus far I'm happy with the choice I made with the 4.10's and with the 300 or so mile trip home I did average 14.7 ofcourse that was the dash telling me.
Sarge












