Perhaps its a difficult theory to prove...but my theory is absolutely that on the whole, the Mark III guns are a solid step below the Mark II's.
I have been under the impression that aside from the LCI and mag disconnect, there are virtually no differences. In fact, I do recall reading that the feed ramp was improved to help with reliability in the MKIII's. Am I missing other differences?
On the whole, I have heard of very few complaints about the MKIII.