Oops, I meant the AZ6 (which was in non-V CTSs), but the main thing I'd be considering is shift quality. T-56 doesn't feel as nice as an AR5 or a lot of other transmissions, regardless of the car it's in.
The stock AR5 is no shining example of good shifting transmissions! Compared to others, it is notchy and sometimes a bit balky. I have old British boxes that I can shift like silk with a couple of fingers, with gear splits about 1400 rpm apart at 7,000 that are a delight (too bad that they have crappy synchro durability).
I haven't driven anything with the successor to the T-56, the TR-6060, so can't comment, although they continue in having a 5 speed with the 5th gear being a normal OD ratio and then tack on a super long (and therefor irrelevant to performance) 6th OD ratio. Wish they'd do what other cars (including a BMW I own) do and have the 6th as a normal OD (0.7-0.8) ratio and the rest of the gears closer together with 5th being the 1:1 instead of 4th.
Looked up the 6060 and it appears that they spent considerable effort to make sure the synchro action was durable - nothing I saw spoke to how smoothly it shifts. Maybe someone that has driven one can comment.