Another 6940 series and Aimpoint PRO fan here. I just added an X300 with a LaRue mount to my 6944, and my initial impression is that it does not take up that much space on the rail. The LaRue mount also has the added benefit of being easier and quicker to remove than the stock X300 mount.
http://imageshack.us/a/img856/4938/p1010067ai.jpg
http://imageshack.us/a/img832/8420/p1010068ki.jpg
http://imageshack.us/a/img267/8706/p1010069yj.jpg
That combination might be worth your consideration.
Best Regards,

