I am looking for a new salsa Fargo, mainly as a bikepacking tool and also light gravel racing. My problem is with the stand over, I have very short inseam(67cm) and long torso and hands for my height (1.59cm). My current road bike has a standover of 69cm, which is the same as the xs on the Fargo. The problem is with all the other measurements, my body is better suited to the small Fargo, which has a stand over of 73cm. I am mainly concerned about safety, since there will be basically no clearance, and painfull dismounts. Should I go for the xs and optimize sizing with longer neck and back seatpost or should I go with the small which I believe it will be more comfortable while riding?
It’s easier to make a small frame bigger than the other way around. The Fargo comes with a very short stem per default. Only 60mm on the XS.
A 90mm stem would put your hands 6mm further forward than where they would be on the size SM Fargo which has 1.4cm more reach and a 1cm longer stem than the XS. Stems are available all the way to 140 or even 160mm length, though above 100mm or so it can result in awkward handling.
Keep in mind that installing a longer stem requires the cables and hydraulic hoses to be longer. So try to order the bike with the stem length you plan to use or ask them to install longer cables.
Don’t slide the saddle back to make the bike “longer”. Seating/saddle position should primarily be optimized for pedaling. All other adjustments are secondary.
Edit: In my opinion the only two reasons you might be inclined to get the SM size is that you can install 3 bottle cages and use 29" wheels (though those would exacerbate the standover height problem).