I have three of the 20" Carr steps on my rig. I like the 20s. They are comfortable to use. Personally, I would be fine with 10s, but I know where everything is, so I don't make missteps.
I've noticed that when other folks climb into my rig, it feels awkward to them--and even more so coming out. They use all 20" of those steps for safe navigation to the ground. The 20s are easier all around, and I suspect they have prevented more than one slip and face plant. No downside, and a lot of upside. For me, the 20s are well worth it.
OMG, the Silver Streak is Sold!
2006 SMB EB45ish.
5.4L, QuadVan 4x4
Ready to Rumble!