I would use lights rather than extra lights.
I don't like extra lights because I don't think they've got enough "oomph" and sound kind of tinny. If you like light, fast strumming, then they'd probably be just the thing. I beat on my guitars pretty hard. I like the sound of mediums, but not how tough they are to do proper hammer-ons and such. So I compromise between extra-lights and mediums with lights.
I usually use D'Addario phospher bronze lights, but I also like the silk and steel, and the nickle if I want something really really bright (which I usually don't).
That's all stuff that should NOT be taken as gospel. When compared to other expenses with guitar, strings are pretty cheap. Plus they're expendable because they collect oils from your fingers and dull in sound pretty quickly if you play a good bit. Given that they're not meant to last and that they're pretty cheap anyway, I'm a big believer in trying different brands, sizes, materials and such until you get a sound you like. You might like D'Addorio phospher bronze lights on one guitar, Ernie Ball medium nickles on another guitar, and Martin silk and steel ultralights on yet another. It's all what YOU like. And the only way for you to find out what you like is to try different strings.
Granted B chord amnesty by King of the Mutants (Long live the king).
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