Mike,

In my very humble opinion, the biggest difference (other than handlebars) would be frame material; the DS Ironman being Cro-Moly, would be a little more compliant road shock wise as compared to the 1200; the Trek would be a bit more responsive out of the saddle due to the stiffer Aluminum rear end.

I presume you'll put drops back on the Ironman, since you were going to do that with your Stumpy project. Personally, I would choose the Ironman; a bit rarer breed C & V wise, and a bit more comfortable. But, it won't have eyelets for racks. You'd have to use a seat post mounted rack for the Rear. The 1200 has eyelets front and rear.