Yeah, it's always a crap shoot. One part can fit great but the whole thing can be killed by something else (small arms, high arm holes, baggy waists etc).
I've recently found a few stores who post the "pit to pit" measurements by measuring across the back, instead of the front, which I'd never seen before. But I've come across it 3 or 4 times recently. Weird.
I just need to be rich and cop first, ask questions later.
EDIT: fwiw this is the cut I am talking about (but one of the older, quilted sleeve, washed lamb versions): http://shop.bdgastore.com/products/busher-double-riders-jacketWarning: Spoiler! (Click to show)