After extensive research, i can confirm that in my case, sp6 hf1 has fixed minor rendering issues that i had in sp6, but the average frame rate is a disheartening 30-40 % lower than sp4.
The route i am working in is really dense with hundreds of self made sketchup bulidings (no lods), and thousands of speed trees. But it works flawlessly in sp4, where i get with my rig ( 64gb ram nvidia 5080) an average of 50-90 fps even in the most heavy areas.
Another failed update....