Stiffer is not always better, it's just stiffer. It was Columbus' attempt to increase stiffness, but it's hard to say if it's really better. Usually cheaper tubesets have thicker walls. Thicker walls make a stiffer frame. Thinner walls are usually the newest and most expensive alloys. They don't make a stiffer frame inherently, but the strength of newer alloys is greater than older products such as 531 and the Columbus Cyclex steel (the steel that SL, SLX, SP, SPX, and early Tretubi were made of). Stronger steel allows thinner tube walls to have adequate safety margins and durability.

Check out the "Magnificent Seven" article: Magnificent 7 - Habanero Cycles

A lot of food for thought here. Also, look on Ebay for a Mondonico. One of the greatest hand-builders ever, and the bikes are very under-priced in SL or SLX. But there is nothing low-end about them.

Re: internal cables - this feature is a product of the frame builder, not of the tubing manufacturer. Plus (IMO) I think one is better off with external routing. It looks less elegant, but holes in the frame tubes can be places where rust begins. If I loved a particular frame and it had internal, I'd accept it, but I would not seek it.

I also agree with relaxing and taking it easy.

Litespeed is usually titanium, not steel. Is that what you want?