The 4.30 gearing is used on the "Tremor package" with factory 35" tires. 4.30 gearing will allow for slower crawling over obstacles than the 3.73 gearing. 4.30 gearing will be (more) fun if you decide to stomp on the gas pedal.
How quickly you drive and how hard you press the gas pedal will impact gas mileage with either set of gears.
GCVW for F-350 SRW 7.3L gas with 3.73s is 23,500 pounds. GCVW for F-350 SRW 7.3L gas with 4.30s is 27,500 pounds.
Ordering will allow you to get what you want while avoiding things you don't want to pay for.
I suggest ordering your truck with a bed. You will receive a "complete vehicle" rather than an "incomplete vehicle". This may help you avoid some issues, depending on where you live.
Maybe I just missed it, but, what vehicle configuration do you want? Regular cab, super cab, crew cab, short bed, long bed? If CCSB, have you considered the "Tremor package"? (need at least the XLT CCSB for the "Tremor package")
As I mentioned in another post, a F-350 with the highest payload you can get will give you the best capability for a range of hard-sided campers.
With the right choice of options, a F-350 RCLB SRW 4x4 has a payload of 4,960 pounds.
This allows for quite a bit of truck camper, gear and people without even being close to GVWR.