SH7091
The SH7091 is a custom subtype created for Sega by Hitachi, derived from the SH4-100 Series.
It is generally identical (and pin compatible) to the SH7750, but has some changes to the data paths for better performance. The SH7091 runs at 200MHz, and has a direct-mapped cache.
As this is both a custom and legacy part, additional information is not generally available.