It is implied in the definition for stress testing that such testing is performed on an existing / already-deployed system. If your SAS Middle Tier software has not yet been deployed--meaning installed and configured--then doing such testing for that tier is not possible.
It sounds like you might be attempting to determine if your proposed SAS deployment will satisfy the demand that will be placed upon it by your users. You might find the following SAS Communities thread, in particular this linked response, useful: Re: SAS Sizing Questionnaire.
If you haven't done so already, you and/or your SAS Administrator should contact the SAS Account Executive for your organization. The SAS Account Executive will be able to help connect you with the team at SAS Institute that handles the sizing of SAS deployments, based on customer needs.