You actually CAN use the element based option when doing optimization, just be aware that it will be much slower than using the statistical option. Our process is usually to use the statistical option (e.g. 2 sigma) for sizing and then when we are happy with the optimized result, then freeze the design and turn on element based to do a final margin check. If there are concentrations when cause negative margins at this point, they can be separated out into separate components for additional sizing (for example, adding padups in corners, etc.)
You can get element based margins, controlling failure modes, load cases, etc. by going to “Sizing Element Results” in the Graphics form.
For the stress reports, you probably don’t want results for all elements, rather you just want them for the 10 or 20 elements with the minimum margins of safety. This will speed up the generation a lot. Very large tables are really what slows the report generation down more than anything else. I would set the stress report options for elements to this when generating the report: