I've been considering putting a wolff spring in my P11, and wondered what the difference would be from the 18 to 19 LB version. Also, a while back I bought a lot of Kel Tec accessories on an auction, and steel guide rod was included. Would it make any difference to pair the wolff spring with the steel guide? I haven't even opened the package on the rod yet, and haven't had any plans to use it with the factory spring. Or, is the steel rod even necessary? I want to try the Wolff spring, but don't know if I should order the 18 or 19. Any thoughts or experiences?