The right side is the same in both cases. The only difference is that the first profile has an additional T-slot. The side T-slot can be useful for attaching shields (in certain configurations), tabs for limit switches, and other accessories like that. The larger footprint is a disadvantage.
Both profiles have exactly 15 mm between the V centerline and the base. With standard MakerSlide V-wheels, this gives 21.45 mm of space between the carriage and the surface MegaRail Z is attached to. That should be enough for smaller lead nuts (a Tr 8 anti-backlash nut is typically 20 mm diameter).
I sent all variants I’m considering out for costing, and I’m hoping to hear back from the extruder soon.