My husband just completed a 1200K rando ride last week. Was a bit nervous the week before, since the longest ride he'd done before that was a 600K. We put it all in equation form:

DFL>DNF>DNS

Although with your strength in running and the bike, I agree, you will NOT be DFL. But I'd still rather be last than at home not doing it. So good for you, Oak! I'm betting a dinner in Seattle, if you ever come here, right here that you'll have a ton of fun.