According to the recent Steven Mead Q&A's, the Sovereign and Prestige differ only in bell thickness and leadpipe design apart from the cosmetic changes. The instruments both use the same valve block, bell taper and overall design.
The Prestige's bell has more mass resulting in a slightly darker sound where the Sovereign's lighter bell responds more easily. The sovereign has a free-floating leadpipe design and bends a little more around the bell where the Prestige has an extra brace between the bell and the leadpipe and is also a tad more straight. These different leadpipe-designs plus the difference in weight, due to the different bells, not only result in different playing instruments but also in weight and feel in the hands of the player while holding the horn.
Personally, I always found the Prestige on the heavy side and fairly "difficult" to play, requiring a lot of practice and air to be comfortable playing one. I picked the Sovereign 967T over the Prestige while choosing a new horn last december, preferring the response (including a very poppy low register) and lightweight feel over the darker sound of the prestige.
As Barry already noted, the Prestige has some extra "bling": gold-plated trigger assembly and valve caps plus some extra engraving under the Besson logo on the bell and a fancy all-black with gold trim case. Besson also includes an extra set of valve caps in the case, these are of a different weight than already installed on the instrument.
The new gold-lacquered Prestige had some improvements made to it including the removal of the extra brace between the leadpipe and the bell. Steven Mead claims these modifications improved tuning and response while retaining a dark sound. I tested one briefly in France before the global health crisis and quite liked it.
In the end it comes down to personal choice of course, build quality and finish is the same on both instruments and they are priced about the same (around €700 difference in Europe).
Have a listen to this short duet I recorded a couple of weeks ago with my girlfriend. I play the Sovereign 976T while she plays her Prestige 2052.
https://www.youtube.com/watch?v=bCCQlu-_QoQ