FortiGate-100F (rev. 1) Upgrade RAM to 8 GB?

So, there are different hardware revisions of FortiGate FG-100F/FG-101F. The first revision includes 4 GB of RAM, the second 8 GB.

=> So, there must be a reason why Fortinet upgraded the RAM of this model from 4 GB to 8 GB?

=> So there are situations when 4 GB are not enough?

Being a user running FG-101F Rev.1 clusters, I have to admit that RAM usage is already quite high: 72% of RAM being used with some IPS enabled, 120000 sessions and combined 600 Mbit/s of throughput and reached. Some weeks ago I reached conserve mode... and deactivated IPS profiles.

To put it in a nutshell: I would like to upgrade the RAM. Is this even supported by Fortinet?