The RIA frames (and some slides from what I have read) are cast. Not that that is always a total negative (Caspian frames are good). The Springfield frames and slides are forged. I have also read a few cases o the 1911 Forum were the RIA/Charles Daley/Armscor are not built to the same specs as traditional 1911 makers and replacement part fitting has been problematic.
For the difference, I would pick up a Springfield GI if it will be a project or a Milspec if it's going to stay stock.
There seem to be a good chunk of folks happy with their RIA's, but I see more folks with problems then I do with the major brands.