Hi,
Check if you have some NET_BUFFER_SZ , SIZE_DATA_BUFFERS,
NUMBER_DATA_BUFFERS in your registry,
Maybee they are too high,
I have get a similar problem, low perf (200 Kb/s) and buffer problem in
bptmetc...
My system was in production I just check network and kernel cpu usage (over
100 %).
I have change the machine to a bi-processor,
 And now backup perf to 6000 Kb/s so very better,
I don't have get the time to analyse why the old machine start to sature
with low perfo (and buffer ).
JM