square-taper cranksets were not standardized to always work with a certain length bottom bracket, so to get the proper chainline for your application, you need to know two things:
* your desired chainline
* the crank you're using
chainline for triple cranks is measured from the bike's centerline to the the centerline of the middle chainring.
standard chainline for road triple (assuming 130mm-spaced rear wheel) is 45mm, and for mtb (assuming 135mm-spaced rear wheel) is 47.5-50mm.
Sheldon Brown has a database of bottom bracket sizes for various cranks. The page talks about chainline as well.
In your case, I assume you're talking about a road bike (I don't think you ever actually say) because you mention 42.5mm chainline on the rear wheel.
I am using the Sugino XD2 (which I think is the same forging as the XD600) and have achieved proper chainline as well as equal spacing (left pedal and right pedal are equidistant from bike's centerline) with a Shimano 110mm bottom bracket. I would recommend that you do the same.
Note that standard chainline for road double is 43.5mm, but 45mm is used for road triples because there are more problems cross-chaining from granny gear across the cassette if the crank is moved too far inward, and because the granny gear can rub against the chainstay on some frames.
If your frame is an mtb frame, you may well need to move the crank further out so you don't bump the chainstay with your granny gear.