"I'm usually a 9-42 guy, and I think the seven-string is a 52. Some of the guitars are tuned down for songs like John the Revelator and Gravity Storm, so for those I use like 10s. Those songs are tuned down a whole step. So even with heavy strings they're kind of floppy. I've used Ernie Ball for years and years. They're a solid company, they're great people, and they just came out with these new strings called Cobalt. It's always been my feeling that strings are strings, how different can they be. So I put these strings on and at first I didn't like them. I thought they were weird. The really feel different - really slinky and pole. Then I started using them and they just started feeling more the way a guitar should feel. So I really liked them... These strings, maybe it's not feel like a guitar should feel like, maybe they're more like what my zone feels like. They move more with my emotional input," says Steve Vai about the Ernie Ball Cobalt Super Slinky Electric Guitar Strings.more
I've tried a ton of different strings when I was starting and felt the Ernie Ball Super Slinky's were the best fit for me. Then Ernie Ball upped their game with the Cobalt series. I only use Cobalts on my FSR Strat. The output goes up, string life goes through the roof, ability to play louder when unplugged, and superior tuning stability compared to other strings. They are more expensive, but they're worth it. Another thing is that they seem to get your fingers a little dirtier then regular Slinky's.