When preparing for the Iron-butt 1000 mile days as well as normal short spirited riding, the seat was a major consideration for me and hence my 2p below:
Looking (have not used one) at the Sargeat seats, they do provide comfort on long rides (as many people would attest), but for my riding style, where I like to move on the seat when navigating bends and occassionaly also slightly change seat positions on long rides, it seemed that the sargeant, with its cupped shape, would keep me relatively more fixed to one position.
Wunderlich and Touratech on the other hand, do not provide custom solutions, but the seats are well contoured to provide support at the correct places and at the same time enabling easier movement on the seat.
I finally went for a Touratech seat and loving it (especailly after completing two IBA rides). Experienced a Wunderlich on a mates' bike and both TT and Wunderlich seem to be the same.
Hope that information helps in your decision.