My father has a DPMS DCM/CMP upper he runs on his frankengun. I am convinced it is capable of shooting up to Master-level without too much trouble. The only things I can say about it are that it has a tight chamber and batters the firing-pin retainer for some reason.
I mention the chamber issue because if you get into doing alot of competition, you will be reloading and the DPMS needs a Small Base die and you should gauge your ammo before using it. Otherwise get one and go shoot.
However, I have an Armalite DCM myself and feel that it is worth the extra clams to find one. Shoots well, is chambered such that it readily digests reloads and has a great out-of-the-box trigger. Once the barrel is gone it is going to a custom smith for some fine-tuning, but it will get to the top without outside help. Also check out RRAs National Match models. They have a strong reputation as well.