SAS strongly recommends consulting with a SAS Sizing Expert to obtain an official hardware recommendation that is based on your estimated SAS workload and number of users. Disk space requirements are provided for individual components in separate documents. However, the space requirements that you can obtain from the individual System Requirements documents that are provided for SAS Solutions and other add-on products are not a substitution for expert advice. To request sizing expertise, send an email to firstname.lastname@example.org .
After some excitement that this was a new way of obtaining the information without having to use the tables provided in previous releases, I sent an email to email@example.com . In either a Comedy of Errors or a Tale of Woe, a technical support ticket was created from my email, but no requested space answer was put forth.
Is this an upgrade in-place or are you installing 9.4M8 on new servers? Organising a sizing review is best done via your SAS account manager in my experience. The screenshot you've provided only refers to space to install SAS software. It won't increase much for M8. You need to size other disk requirements as well like WORK and application data although what you are using now would be a good starting point.
Sizing also covers number of cores / CPUs and memory. Again what you have now is a good starting point. If you still have a lot of headroom with CPU and memory usage then there is no reason to increase these.