Well, I can't answer everything, but I have the LowRider MAX and I enjoy it. I gave up when I first started looking and just called Yakima. The guy explained that the LowRider was the first iteration of the two. It had a generic clamp meant to cover most factory racks. He said the X and a few other new factory racks had too large a diameter, so they came up with the LowRider MAX, which is the same idea, but allows a custom fit "claw" part that you order according to your vehicle type. The claw (#2 for the X I think) fits perfectly, and I'm very statisfied.
I can post some pics if it helps, here's the best I have right now...
Anyway, I'm curious if you can mount the lowriders upside down, to gain back some space...
I'll have to eyeball it tonight.