I see your pre-requisite was imaging and soundstages well, with decent bass extension and you like rock music.
I've owned a pair of Alon IV's for many years and loved them, I've also listened to the Alon V's and Alon II. The Alon V was probably the most refined out of the bunch, but they're getting up there in age. So compare similar Nola products. I've also auditioned many Totems, Proacs, and Vandy's, and have always left impressed. I'm also a fan of Revel, but the ones I Iike are out of your budget.
I think you could group the Totem and Proac in a similar category. Tight bass, qood dynamics, good resolution, and images very well. The soundstage won't be as deep as the Alon or Vandy's.
The next group is the Alon and Vandy with a similar design concept. The Alon uses an open baffle design that creates a huge deep soundstage, very open sounding with good bass and imaging, but you could lose a little focus with an open baffle design, but you gain some transparency. The Vandy's also have something similar to the open baffle design, depending on the model that you're interested in.
I think you'll have to compare the Totem to the Proac and the Alon to the Vandy.
The Thiels are great too but not as good for Rock Music, Theils can be a bit lean in the bass.
I've never heard the Usher's, but their reputation speaks for itself. I'm not sure you will be able to get deep bass with an Usher in your price range, unless you step up in bucks.
You may want to throw the Gallo Nucleus reference 3.1 into the mix; very focused, huge soundstage and deep tight bass, and your McCormack should be able to handle it. I think that actually hits all of your pre-requisites in one speaker.
Good luck and please keep us posted! (Pun Intended)