I am running the SW 180/240 secondary spring but I don't ride below 8K very much. The 160/235 secondary spring was for riding in the 5K range I believe.
Looks like you have the right primary spring.
I thought I posted this at the end of last year what I found to be the best setup I had tried but it must not have posted. Here it is.
SW 160/250 Primary Spring
SW 180/240 Secondary Spring
Straight 48* Helix
SW S1T Weights 74.6 gram
TKI Belt Drive 28/63 ratio
I also have two glide washers in with the primary spring
This setup will run 8350 all the time on my sled. I would like to try a set of heavier weights and see if that will bring the rpms down just a bit. I doesn't seem to matter if I am at 8K or 10K it runs 8350. I would also like to try a 29 or maybe a 30 top gear for the belt drive. It seems like the higher I gear it the better it performs and I don't loose anything on the bottom end.