We have a 75GB DB at 90% capacity.  It takes a while to do a full backup to
a 3590 class tape device.

We have enough nodes dumping data at the box that the log can fill in the
time it takes the db backup to complete.

We have our incremental trigger set at 40%, so incrementals have (so far,
knock on wood) been completing OK, provided no other problems occur, such as
the problems with lock contention in the 4.2.2.x  series.