Chris is spot on, I had a Rheinard 10x1 (didn't I buy it from you Mr Long?!
) which I tried the Rheinard springs in and I took them out after one run, they were useless in a buggy.
I always used to run my V2's with a med-hard spring on the negative and hard spring on the positive brush, like Chris I always run sprint edge brushes in them too.