You say the wife would like a physically smaller machine, which pretty much rules out the Suzuki KQ450 (best 450 imo - get her on one before you make up your mind) due to it using the same chassis as the KQ700.
Look at the Yamah Kodiak 450 IRS/Grizzly 450 IRS for more utility than sport, or the Wolverine 450 (based on the same motor/transmission as the previous) for a little more sport than utility.