I have just created a Service Request asking about Standalone 3100 with SSD and the answer was positive. However...
Looking at the sk110052 it says: Solid State Drive (SSD) is supported with a Standalone Deployment only on 3100/3200 appliances.
At the same sk110052, three lines above, it has a confused text saying: When using Solid State Drive (SSD), the local logging feature in SmartConsole is not supported on the Security Gateway. In case of a disconnection between the Log Server and the Security Gateway, logs will automatically be saved locally on the Security Gateway. So it is contradicting itself in the same paragraph.
Why the Standalone is supported in the 3000 SSD family but not in the other appliances (from 5100 up to 5800) using the same disk (at least they have the same size)?