What would be a reasonable fps and millisecond goal to set for this machine to run on epic settings 1080p?
I feel this question is the wrong way round. You firstly need to decide what framerate you want, and then change the game and settings to reached that frame rate. Depending on your scene and game, you will have to change your settings and lower resolution, which also depends on your targetted hardware.
The screen percentage (r.ScreenPercentage) can help with performance by lowering from 100. Also, dynamic lights are expensive in general, so using baked lighting were possible is usually the best approach.