The S-7 is leaner than the S-8. I would try the S-8 first. What altitude are you at? I know Bedell99 runs the S-8 nozzle with a leaner-than-stock needle (30-76 vs. the 30-74,73 that comes with the bike). FYI, he is at about 5kft. I haven't figured mine out yet or I'd post my results. As soon as it warms up over here I'll get the chance.
i live some where 2500' i guess, i'm running a 400 main 27.5 intermediate and a 30-74 needle.. i have had the cylinder ported and put on a cool head with an mx insert and weisco piston...
I would personally go with the s-8 nozzle. I have no problem with my jetting at approximetely 5000-6000ft running a 30 pilot 30-76 needle and 350 main. Air screw adjustment is critical on this bike. I found that running a hotter plug during the winter helped out tremendously for goop, but will continue to run the standard plug during the summer. It has been cold here in Denver as of late. So the bike takes a while to warm up and I have been getting excellent readings with a BR7ev. As for running the S-7 I would recommend you " richen" the low end circuit especially at "only" 2500 ft.