Hi,

I see you have already obtained many
good recommendations.

Another 2 cents:

do even better job in analysing what exactly your bottleneck is.

If it is CPU, than exclude/include list processing against your 
large directory trees might be the problem.
Try to simplify the list.
Divide the backup into smaller chunks (backup separately
the subtrees on your file system instead of whole file system).
From my experience I can say that a backup from 2 filesystems
with 500.000 files is much shorter than backup of one filesystem
with a milion of files - maybe it is true with partial backups as well.
This approach will save your RAM as well.

I do agree with most of proposals you already received,
pick the right one for you
good luck!

Juraj SALAK
Linz, Austria