Some points are not clear in your question:
1. comparison of Eb/No and Es/No doesnt give you coding gain. Comparison of any one of these with and without the RS gives you coding gain.
2. The QAM doesnt contribute to any coding gain. Are you talking of bandwidth reduction in comaprison to some other modulation scheme?
3. Eb/No Vs Es/No is usually a fixed relation. You could calculate the probability of symbol error given probability of bit error. However, this has no relation ot coding gain.
-b