Name: RS690/RS740 Host Bridge
I investigated a bit further, and didn't find much information. Looking into the things others have gathered at Wikipedia, your findings seem to be accurate, AlbertP. It's clear that there are no differences in programming between RS690 and RS740 chipsets, the practical difference being a higher possible clock rate (500MHz instead of 400MHz for the graphics part) due to the smaller structures.
So I now suggest to name this subsystem "RS690/RS740 Host Bridge" to make clear to the average user that it is nothing special. The 7910 differs from the man ID 7911; thus even those "lspci" implementations which use the main ID as a fallback would regard this as an unknown ID otherwise.