Bryston 4B-ST or 4B-NRB?

Anybody had experience on both of the 4B? How much difference between them? Thanks for all the replies.
There is a substantial improvement in the circuit design of the 4B-ST (the "ST" stands for Stuart Taylor, the electrical engineer who designed the new circuitry). The 4B-ST has roughly an order of magnitude less THD and IMD than the NRB, which is audibly noticeable on well-recorded CD's. To my ear, the "ST" version is also more dynamic, with greater transparency, better bass response, and improved treble.
Have to agree with Sdcampbell on this one. Having owned various Bryston gear over the last 12 years or so I can that the ST series is their best bar far. If you wanted a good strong amp for a home theater application where the desire is to reproduce action packed scenes with little regard to quality of sound then I think the a NRB version would do you fine. If you are at all interested in the quality of the sonics then the ST amp is the way to go.
ST has better transparency in its mid and hi frequencies. The sound is a bit cooler. The NRB is slightly richer in tone but lacks the detail. If you're using it for mainly power NRB would be a good pick for the cost. If you're using it for full spectrum, ST would be more satisfy.