Viper RT nuts.. what line do you use?

[viper7mi]

I finally took the viper out this week and rode 240 miles and it was great. I have the yamaha RT nuts on the transfer rods on the 2nd line. The rear of the sled had alot of fish tail action. What line works best with stock sled and skis?
Thanks

 

[koodat]

Book says line 3 is stock with stock adjuster nuts.