Are you talking about the "E" at the end of a Colt's serial number?
If so, this is my meager experiance:
I own a Colt Combat Elite, "Enhanced" model, that I purchased in 1994.
It is basically a poor man's Gold Cup. It has the target sights, better parts, better fit, nice factory trigger, etc. It reminds me of my friend's "pin" gun.
I have seen other Combat Elites and they looked more like the 1991A1 with a blued slide over a stainless frame. The parts weren't as nice and the fit was so-so. I spent $1000 for it and it shoots better than I can.
I hope that helped some.