Trying to size a header what can I do?

I have a house that is 28 feet deep (about) it's a cape cod with a somewhat finished attic. The floor joists for the attic (or cieling joist for the main floor) are spaced 16" o.c. and are 2x8's. Obviously the 2x8's don't run the whole width of the house with out hitting a support wall. However there is a stairwell to the upstairs and the 2x8's run from the outside wall to the stair well wall(10ft or so), which is built in Face Framed 2x4 including the top plate and the 2x8's rest on the face framed 2x4 wall (not nailed to doubled up 2x8's like in normal framing). I would like to open up the stairwell and header up the whole stair well wall. So one beam would hold all these floor joists over an 8 ft span. This is in wisconsin so assume snow load and maybe 40psf since it will be a living area above I guess. It looks like if I'm reading the span table right that I'm going to need 3-2x12? Is this correct or can I get away with 2-2x10? Worst case scenario I can put one colom in the center If I need to. And yes all the supports have been worked out in the basement area to compensate.