I have a gen 3 G35 that I added a non captured tungsten guide rod from zev (glockworx). I am using the ISMI #15 spring. I like it. A little extra weight. But I will say that I am starting to see a wear mark around the guide rod about 1/3 of the way back from the muzzle. It is not bad but it is there. I think I read somewhere that others have seen this. I do not know if I would be better off with the red zev spring instead? I will probably just keep the ISMI. As for extensions, I am using Dawson. They work well, and seem to be made well. I am getting +4, but I can force +5, it is just not re-loadable for me.