...5lo/5hi splice boxes are the same as a 10-speed with "really short ratios." In fact, the two gearboxes would likely have the exact same ratios. O_o

The only difference is that you have a standard 5 speed Gearbox (With splice) configuration for one, and for the other you have a double-wide 10-speed |-|-|-|-| for the other. You can see why most gearboxes with more than 10 gears use a splice or a foot pedal configuration of some kind. I'm sure QuickDodge could provide alot more input here though, considering I don't have my CDL.