OK...I see alot of reads here but no posts. I guess like me, this is a subject of little knowledge. Perhaps I found the answer in a letter to Specialized Armament Warehouse. As you may or may not already know, they are a stocking distributor of Colt parts. Perhaps the largest stocking distributor in the country. Either way, I got a quick reply from "Tera" to my query and it reads as follows...
The forged extension is made from high quality 7075-T6 aluminum whereas the
extruded extension is made from 6061 which is a much softer material.
Practically speaking, the extruded receiver may work fine for you but the forged
receiver is the military proven part used on current production M16 rifles.
I placed an order for the the forged 7075-T6 assembly. Kinda pricey but at this point I haven't had a reponse from any other souce I've tried. So there it is if any one wanted to know about this minor subject in the world of AR's. Again and as I've stated before, I tend to over do it on my weapons. It would eat at me constantly if I settled for a sub-standard part and left it to chance that anything might go wrong whilst I battle paper targets at the range...yeah my kids will tell you I am OCD but hey, you gotta have a hobby!
Are you sure it isn't time for a "colourful metaphor"?