[robespierre]

Only the R3010A FPU is marked as a 25 MHz part; the R3000A is marked for 16 MHz.
This sounds like 4D/80's IP4.5, except:

The memory complement. A.J. Corda's This Old SGI page says about the IP4.5:

Integrated CPU memory on board (8 - 16 Mb), Standard 30-pin 9-chip SIMMS. Memory was expandable beyond 16 Mb by use of a companion VME card in the next slot which connected to the IP4.5 via an external bus jumper plug.

the IP4.5 has a large bus-type connector on the front of the card which is not found on an IP4.

and the audio section:

The output from the audio section is provided by two 1/8" audio jacks on the IP4. The IP4.5, on the other hand, uses a 4-pin connector. Both are located on the upper back-edge of the board (as seen from the back of the cardcage.)

This mystery card has three audio jacks, and no bus-connector on the front. It also has a DB25 (?) port, possibly for a parallel printer interface: if my sources are correct, only the VME embedded processors (V30/V35) included these on the card. But this card has no metal I/O panel and uses traditional SGI-style ejector levers, unlike the embedded boards.