I've used a Quest spring in a B3 and vise versa. They both measure out about the same. So close that if you held them next to eachother you couldn't tell the difference. The Quest spring is a little stiffer though. It DID give my B3 more uumph, but it got a bit more hold sensitive. With the leather seal, it took 2 tins of pellets before the excessive dieseling went away. Until then, velocity wasn't quite consistent. She was ALLOT better with a synthetic seal and the Quest spring.
There was someone else here that did it, but I believe he reported the South Summit spring in a Quest. Tests turned out near identical numbers between the Quest Spring and the QF2 Spring in a Quest.