Most of us carry the standard SS114, and the traditional looking SS154
The SS164 has less of a dish then those two, and can be seen with some of the new one-piece toilets from Toto.
I have ordered some SS164's for stock, but they are still selling them with the one-piece toilets at this point, and I guess they don't have enough for stock orders of just the seat.
With the Vespin, you would want either the SS114 or the SS164
The SS164 is now the new SS114