Incredible trip. All the people associated with RwL are incredible; took great care of us, and the guides rode hard. They did a great job of keeping a fast pace for the faster guys, but never asking anyone to ride above their ability - always multiple guides, tail rider and key stops for a rest (you'll need it) and great photo ops (bring a drone if you own one!). Iceland is a truly wild place, so know that the mountain huts are just one big room with lots of bunks - very comfortable, very clean, but no private space - you are WITH your group for the entirety! I would do it again in a heartbeat.
Honest self-assessment: I'm a 25+ yr rider with a bunch of dirt experience, but certainly not a full send guy (what I lack in technique I make up in brute force, and by not riding beyond my ability) - 48yrs old, pretty decent shape - I rode back of the fast group. If I could offer you one piece of advice: LIFT before you go; squats, traps, shoulders - the rocks were unreal. This is a real adventure, not a tour.