EC2 instance type recommendations and performance benchmarks for FortiGate

So far this (https://www.fortinet.com/content/dam/fortinet/assets/data-sheets/FortiGate_VM_AWS.pdf) is the only document I've found that compares FortiGate performance for different EC2 instance types in AWS. Is there any other documentation that compares performance between different generations (c5/c6/c7) and processor types (c6i vs c6g, for example)? The on-demand pricing per hour for a c6i.large (or a c5.large) instance is 25% more than for a c6g.large, which is not insignificant.

And why does documentation for the AWS FGT 7.0 recommend c6i or c6g, whereas 7.2 and 7.4 recommend only c5?

https://docs.fortinet.com/document/fortigate-public-cloud/7.0.0/aws-administration-guide/261537

https://docs.fortinet.com/document/fortigate-public-cloud/7.2.0/aws-administration-guide/261537

https://docs.fortinet.com/document/fortigate-public-cloud/7.4.0/aws-administration-guide/261537