I have a hybrid lightning madness spec for my SI. The only spells I use playing solo are death field when ever its up, affliction, spam lightning barrage. When you get an instant cast proc I use crushing darkness and when thats on cooldown chain lightning. I never use shock at 50 unless I am in pvp and want to finish someone off with low health. I setup an isboxer macro to always activate my two relics. Anyone boxing SI should spec the madness talent so lighting barrage has no cooldown.