With Stalker gear it's so easy to hit 40% crit (with agent 5% buff), once you get enough pieces buy more pieces with mods and enhancements that contain power and trade out some crit for those until you get around 35-36%. As the above said, try and get surge to 75% as well.
But crit is what makes madness work, since you get heals on crits and the dot crits are bigger.