Well, I'm fairly light at 140lbs, and I've owned and toured with both a cross check and an LHT, so maybe I can provide some insight. I think if you plan to tour a lot and you plan to go to south america the LHT with 26" wheels is a no brainer.
In my opinion there are still huge benefits to using a dedicated touring bike even for a light rider. It's not your body weight that makes a big difference in the bike's handling, it's when you start attaching panniers to the bike. I've toured with a full load for camping on a old hardtail trek, a cross check, and an lht, and the lht was definitely the most stable with all that weight on the bike. The long wheel base really helps stabilize the bike, and gives you the confidence you are going to want bombing down a mountain road with full camping gear.
While I slightly prefer riding my cross check for commuting and an unloaded centuries, the lht is still a great ride. I don't think I go any faster on my cc, I think it just feels a bit faster because the handling is snappier.
No bike is perfect for all situations, there always compromises. That being said I think a 26" wheel LHT is pretty versatile bike and an ideal tourer/commuter/whatever bike.