Okay, my take on this, I would guess I’m probably in the top 50% of riders speed-wise. I can cruise at 14-15mph on the flat, and can push up the pace to closer to 17mph if I’m in a hurry for a couple of miles, but I can’t keep that kind of fast pace up forever. It’s important to be able to keep up this kind of pace after you’ve already ridden 20 miles.
As a basic thing, I’d think it’d not be worth entering (at least to compete) if you can’t average 12mph/20kmh for an hour, proper average that is, ie. you start somewhere, and 1 hour later, you are 12 miles away from where you started, including any rests or stops.
I’d suggest you really want to be comfortable with riding 110 cranks on the flat, and 125s in hills.
If you really ride 200 miles a week(!) you’re going to get very fit very quickly, and learn the skills pretty quick. If you have that much time, I’d spend the first 800-1000 miles just learning to ride the coker, the next moving down to 125mm cranks. Then concentrate on speed, and spinning reliably at speed. By this point you should not be falling off the coker ever.
Also be careful with riding those sort of distances when you’re starting from a low base that you don’t screw your knees. If you get hurty knees, don’t ride through it, dump a few training rides, it’s a sign you’re training too hard, and you’ll end up with buggered knees if you’re not careful, which is pretty much the worst thing that can happen to you in a race like this.
You may also find it beneficial to cut down the distance at times, and concentrate purely on speed. If you’re willing to ride a lot, getting endurance up so that you can ride the distances is not that hard, whereas increasing speed takes training. Bear in mind that the distances in RTL are not super-large, and you only have to ride a third of the total distance, so it’s more of a middle distance race than a long distance race, and pure speed will be at least as important as endurance.