Colnago has been offering CX frames for a long time, I would not doubt that this is one.
One inconsistency that caught my attention in your descrition was the 7-11 chainstay protector. THe protector at casual glance appears to say 7-eleven.com but remember that the 7-11 pro team was way before the internet, they would not have had a website during era of the 7-11 team. Looking closer, it actualy reads 11eleven.com which is aparently website for an Itialian bikeshop.
http://www.11eleven.com
THe aheadset (rather than threaded) steer tube and the unicrown TIG fork definitly indicate that this bike is from 1990's onward, it could even be much newer than you are thinking. What diameter are the downtube & top tube? Any indication of tubing used (such as columbus spirals inside the steertube or SLX spirals in seattube?)