Changing the priority level in the performance section of the dnet client usually makes little difference to the performance. It usually just makes the PC less responsive.
To maximise your output, you should prevent as many background programs from running as possible, like the icons next to your clock (assuming this is windows). If it's a box that several people use, you can install dnet as a service, so that it runs even with nobody logged on, but the cow won't appear in the corner. I would recommend running a "checkpoint filename", so that in the event of a system crash you don't lose the current packet. Go to 2,4 from the main menu & choose whatever name you like (eg dnet.chk).
You should also increase the maximum work unit size to 2^33, instead of the default 2^30. This reduces the overhead on the dnet servers as you are sending & recieving fewer packets each time. Go to 2, 12 & 33.
Russman