SRS,
I have never seen a formal comparison done, you will probably have to do the actual comparison yourself.
There is a boatload of info about MRP, you have your choice of sources to get insights about this.
DRP is a little more difficult. DRP in ECC was pretty much abandoned by SAP quite a few revisions ago. DRP now exists in SPP. However, it is getting harder to find info about SPP any more.
There is a doc "Manage Operations for Service Parts Planning with SAP SCM" which contains some high level stuff about DRP you may find interesting:
https://websmp209.sap-ag.de/~sapidb/011000358700000398482010E
If you don't have S* access, you used to be able to see the Building blocks for SPP RDS in help.sap.com. I haven't checked recently, but last time I looked they were there.
SAP Service Parts Planning rapid-deployment solution
If you want these publicly available docs, I suggest you download them immediately. RDS stuff seems to have a way of disappearing from help.sap.com from time to time.
Best Regards,
DB49