I just tested the latest WIP on a realistic typical large-ish scene using my default custom display mode - shaded, no isocurves, thick edges.
File size: 1.31 GB
Number of visible objects: 8 130
Polygon count: 5 380 237 quadrilateral and 6 736 397 triangular
TestMaxSpeed results - Time to regen viewport 100 times:
RH6: 21.01 seconds.
RH5: 58.67 seconds.
That’s pretty good! 
Of course, that will just make me put much more of the overall system in one scene - something that hasn’t been possible until now. I’ll will therefore probably not experience any speed improvements in RH6. 