CIFS backup isn't fun... for DR is it because you may not have a NetApp or other ndmp device to restore to? That sounds like the reason which makes sense...
Do you have VSCAN enabled? That often can be an issue... you can create new shares to the same data path using -novscanread or -novscan and use those paths if that is the case... vscan can slow it down... also make sure e0M isn't being used but probably isn't... I wouldn't expect much throughput of a cifs backup... and would consider getting a small FAS2040 or something for the DR site so you can use NDMP if that is the reason not to use ndmp.
Also are there millions of files? ndmp would have the same inode count slowness if a large file count.