My FIL works at BMC. I actually did what you said but their Dallas contractor never called me back, so I ended up finding my own guy who came out, measured for the windows, and then would installed them. BMC's window division is in Houston (where in-laws live), so I went down to pick them up and bring them back. Guy had a 2 man crew come out and install the windows. Problem was (unbeknowst to me at the time) they were 2ndary contractors, they installed a few windows, told me one would fit b/c it was too big, and wedged a few into place that I later found out bowed the frame so the window isn't completely sealed. I tried to get the original guy to reimburse me for the windows that never fit, never could. /CSB
I guess the lesson is make sure you find a guy who you can trust for measurement and install? Or pay a bit more to get the job done right. Anyways, if you want my BMC hookup, PM me.