Well, no wonder my friend's Salsa 26er (Ala Carte) feels so small...I just determined that it's the 12.5" size (with an effective 20.5 top tube), so it's like an XXS! We had to yank the seat post as high as it would go and it could probably still stand to go a bit higher.

I can't find the exact size chart for my '09 Cdale F5 Feminine, but I assume it's pretty similar to their current WSD Trail SL in a petite/XS. That has a 13.8" seat tube and 20.5" horiz. top tube (so the same as the 12.5" Ala Carte). The S in that bike has a 15" seat tube and 21.7 top tube.

The S Cdale WSD Trail SL has a 15" seat tube and 21.7" horizontal TT.

These are all 26ers, so I don't know how differently the set-up/fit would be on comparable 29ers.

The size S Mukluk I rode has a 15" seat tube (same as the XS, actually) and a 22.8" effective top tube. The XS is 22.2", so not a whole lot of difference, there. Standover was good on the S.

The S El Mariachi has a 15" seat tube and 22.83" top tube. The XS has a 14" seat tube and 22.24" effective top tube.

So...not a lot of difference between XS and S in the Mukluk or El Mariachi. I guess my biggest concern is toe overlap (I wear a wide 8.5 women's...40 men's shoe and tend to position my cleats pretty far back on my shoe, putting my foot more forward on the pedals). I didn't have it with the S Mukluk.

Wheelbase for the XS vs. S is 42.0-42.7 vs. 42.2-42.8 (I think the range is due to the ability to switch between a rear cluster or SS)...so, again, very little difference.

I don't know if my femurs are relatively long, but I sorta suspect that they are.