right from the get go...
http://www.somafab.com/doublecross_one.html
vs
http://salsacycles.com/bikes/casseroll/
and/or
when you look at the opening page for Soma's Double Cross
http://www.somafab.com/frames.html
you'll notice that in both descriptives for Soma's Double Cross that they state both frames will accept MTN or Road hubs.
that is a reference to the rear hub spacing: which is... road at 130mm MTB at 135mm
so my gut reaction is that the reality is the frame is probably spaced at about 132mm
while this may or may not be a big deal.
looking at the chart:
http://www.somafab.com/geometry03.html it states the rear dropout to be 132.5mm (which is how this frame accommodates road or MTB hubs)
as the Casseroll is clearly stated to have a 130mm rear drop out...
it really depends on what wheelset you'd like to use
which really starts to pin point the wheels...
the Soma uses a pinch clamp binder for the seatpost that is brazed to the frame
the Salsa uses a seatpost binder,
collar that is separate from the frame.
its a minor detail, but if for some reason you have an issue, i.e. it breaks! at least on the Salsa you can simply stop at a bike shop and buy a new seatpost collar and be on your way.
whereas, the Soma... well... you'll be needing to have that welded.
top tube length: The Casseroll is shorter than the Double Cross
which means that for a given "fit"... reach to the bar...
the Salsa will have a longer stem
vs
the Soma a shorter stem
what this translates to... is steering responsiveness...
generally speaking... simply in terms of the length of a lever...
the longer a stem... the slower the response
the shorter a stem... the quicker the response
when you look at the fork specs:
salsa fork offset at 50mm
Soma fork offset at 44mm
the salsa places the axle more forward
the Soma closer by 6mm
which makes the steering feel more "responsive"
so you can see that literally these are two different bikes.
one a CX bike the other more of a mix between road bike/touring bike... "non-competitive road riding and commuting to ultralight credit card touring and randoneur rides." <---straight from the Salsa website.
in light of what a bike comes to... depending on your area... I'd think about resale...
a CX bike is apt to resale faster than a Rando bike...