Also check out CIRREM if you like "fun". 100k gravel race in Des Moines in February. Limited number of spots so it fills up quick. It sounded like a good idea in October- luckily I just missed the field.
I did CIRREM in 2012, had a conflict this year so missed it. It was a hoot. Hard, awesome.
Best gravel race I've done was the Almonzo 100 in MN. It's a beautiful thing.
Dirty Kanza is on my radar, but not certain I'll do it.