The Superfly (or maybe the Old Man Mountain - they look like the same tarp, but I like the Superfly color more) looks like the way to go. I don't mind an extra six ounces for the doors, although if I'm backpacking it'd be a different story I think.
As for leaving the bike out, I realize I could and it wouldn't a be a big deal (aside from the Brooks saddle) but I don't like having to re-lube the chain all the time, and I figure being in the rain more than necessary can't possibly be a good thing. Of course, there will be days of riding in the rain non-stop, but still. But the main thing is I like getting onto a dry bike, and an overnight downpour could be fended off by having the bike under cover.