9.8 to 10.1 will be a direct upgrade without any interim release. There are no OOTB tools provided by SAG to perform load testing but there are ones like WmProfiler, SKYProfiler etc, which can help you to analyze the issues with your IS. Refer to the upgrade guide, readme, and release notes before the start of the upgrade and comes with an upgrade strategy.
The load/volume/performance testing should be carried as part of the upgrade project timeline and it should be done on a QA or Pre-Prod servers replica of Production after moving the code/configurations as-is from 9.8 servers with two or three times the current load.
If you want more details about SAG load testing reports, refer to Technical Reports on Empower as they are out for 10.1 version.