If you're going to cut through Utah on I-15 for most of the way then I'd strongly suggest coming on down to Cedar City and taking Utah 14 over Cedar Mountain to 89. Nothing against Beaver (it's a nice place to visit any chance you get) but you might find the extra 50 miles to Cedar worth the ride.
If you take 14 over from Cedar then you'll run by Navajo Lake and Duck Creek, which are between 8500 and 10500 feet in elevation. It's a GREAT ride up 14 from Cedar City. You will literally go from high desert to Alpine forest in the run. And the views are spectacular. This first shot is looking south toward Zion National Park from one of the many great pullouts along 14 ...
Also take a look at John's (jmcollison) posting on another thread with some pictures of Zion ...
http://www.hdforums.com/m_2494599/mp...tm.htm#2500028
One of my favorites is his picture of Cedar Breaks, which you can get to on the 14 loop or by cutting back from 89 ...