Thats is the purpose of the speed cap. To raise the SNRM. No you lower your bandwith which in turn raises your SNRM.
End result = positive DLM intervention
I dont think capping the speed affects SNRM in anyway at all mate,are you on fttc?you cant touch things like SNRM on fttc its a fixed profile,adsl profiles with certain routers like the billion i think it is you can manually change the SNRM