I've used both, and Slinmax is the easy winner. I'm currently logging it right now, but the way my body has been responding to carbs with Slinmax is incredible. I've been able to eat more carbs and stay lean, and I haven't felt the 'carb bloat' since I started this log. Even after a huge bowl of oatmeal I still feel lean and tight.
Performax is really changing the game, they have great products. I was a big fan of Hypermax XT, and Slinmax is exceeding my expectations. To me Slintensity is a basic, bottom of the line GDA. Slinmax gives you much more for the money.