Ah, but 531 (manganese-moly) probably isn't as strong as 520 (chrome-moly), as the "lower" specced tube is most likely welded instead of brazed.
There was a test done (which I can't find now) where teams of professional cyclists were given otherwise identical bikes made of 531, 653 and 501. They universally chose 501 as the most comfortable. That's what you want in a touring bike.
Higher numbers != better for the purpose intended.
I don't believe that's true. What more money buys you is more polish, lower weight and better seals, often at the expense of durability. This wasn't true in the past - XT was meant to be the very best that Shimano could build. I think they lost their way a few years ago when they started making the bearings smaller. That's a poor choice for a touring bike.
In fact, you could argue that for a bike like this a lot of low end stuff is better than high end because it's much more tolerant of poor setup.
With regards to sizing - there were so many made I'm not sure I can give you a sensible answer other than I never bought one I didn't like.
I gotta tell you all something, but Chris667 is ABSOLUTLEY CORRECT! At least to a point. You don't want the absolute cheapest components, but you also don't want the higher end stuff either, low mid to mid-range stuff for a touring bike is where you want to be, and believe or not, even for a non-touring bike of any discipline mid-range is where you should be unless you're racing it. Mid-range stuff is built to be durable, which is why they're a bit heavier. This is especially true in today's world, now back 30 years ago, the higher end stuff was built to be more durable, built to last longer, etc, but in today's world that's not the case, they build the high-end stuff to be light and, in that process, they don't last as long. Quite frankly I think the mid-level stuff has great seals, so I don't even think seals are an issue. Also 30 plus years ago the higher end touring stuff was designed to handle more gear ranges which is why good touring bikes always had higher end components, this isn't the case today, when even lowend components can handle wide gear ranges.
9 years ago I bought a Lynskey Titanium bike, I wanted the comfort (I'm in my upper 60's so comfort became important) of the TI frame which is a real thing because my friend has a TI bike and I rode his bike a lot to get a feel for it before I bought mine. If I could afford a TI bike I could afford to get one with all the high-end components, even a high-end TI frame...but I didn't fall for that nonsense, nor wasted money to do that. The other thing I didn't waste money on was wheels, the place where I got the bike from (Adrenalin Bikes) the guy asked me what kind of riding will I be doing, just riding on rough streets because where I live the freeze and thaw cycle messes up roads bad, he advise to go with Shimano RS100 wheels, they're cheap but are built to hold up to abuse, and so far I have not had to even true those wheels.
I got the lowest end bike Lynskey sold back then which came with 105 components, that stuff has performed flawlessly. Speed up ahead to 3 years ago I bought a touring bike, again I could have spent thousands on a touring bike, but instead I spent $1,400 for a Masi Giramondo 700c, this bike has low mid level stuff, the derailleur is Shimano Deore, nothing fancy, just plain Deore with no letters after it, but it works great; it even has Microshift bar end shifters which are probably as cheap as you can get, but all they have to do is pull cable. Again, with this bike, cheap wheels, because they're built heavy and stout to handle heavy loads. I don't have a lot of miles on this bike yet, but I haven't had any issues, nor expect any.
The other advantage to buying low to mid-level components for touring is if you should crash and break something, or something just fails, and you need to buy a replacement part while on a tour, it will be a lot cheaper to fix. Also, there are a lot of fancy bling stuff for touring bikes if you need a part, you will have to order it from the bling company that made it and wait for it to get to you, whereas low to mid-level stuff is stocked by all bicycle shops. A lot a bicycle shops may not have a high-end Shimano or SRAM, especially outside major cities, they may have to order that too, so you'll have to wait.
