There is a guy over on bikeforums that does a lot (understatement of the year) of hill climbs and posts stats. I asked him what he thought of Ebbetts and Monitor.
I think Ebbetts is nicer than Monitor. It's more gradual, shaded, pretty, and there's a campground with water and toilets at Silver Creek. Monitor has virtually no shade, so the bottom portion of the climb is hot and dry.
For stats...
Ebbetts: 12.6 miles, 3000', 4.4%
Monitor (west): 8.2 miles, 2600', 5.8%
I like high desert also but will the bottom of Monitor be too hot? You've said it hasn't been cooling off up there. At least the stats for Monitor aren't god awful, just awful. :D