I think the sweet spot in the TA lineup is the Reference. Yes, it gets better above that, but it becomes prohibitively expensive for most of us. If you have Sasha's, they deserve Reference
I hear a nice difference from my previous Super's. I guess I didn't try Ultra though. But Reference is where they start "tuning" or impedance matching your components. I think that's what makes them a bit more special.
Try to get your dealer to sell you B-Stock Reference. It doesn't come around very often, but it can save you money.