I used Helicore Hybrids and Spirocore Weichs on a Kay for eight years, playing them every day, and a lot of them were hot and humid outdoor gigs. It sounded great, I have a demo somewhere. Spirocores you just have to play them in and be patient. Helicores are also fine but you'll find different opinions. Right now I have Spirocore Weichs 3/4 I got from another bass I bought and sold and kept the spiros. I've been playing the same since september 2012, they sound great.