Aluminum frames only weigh about a pound more than carbon frames. What makes aluminum bikes heavier is that they usually come with cheaper heavier components. If an aluminum bike was set up with lighter high-end components, it wouldn’t weigh much more than the carbon fiber version with the same components. In addition, I’ve never been able to discern any difference in frame stiffness between aluminum and carbon fiber. I would love to see more aluminum bikes come with better components. Assuming they both cost about the same, I would rather have an aluminum bike with better components than a carbon fiber bike with cheaper components.
If you’re like me and you like 29+ tires, the Trek Slash has a huge amount of wheel clearance and would easily accept 2.8in (or 2.6in) wide tires. If you wanted to ride a 29+ Slash, all it would require is a change of tires. I almost bought the Slash but then the 29+ Trek Full Stache came out and I bought the Full Stache instead. The Full Stache has clearly demonstrated that 29+ and long travel do mix. Riding a 29+ enduro Slash would be a hoot!