Honored Contributor
Honored ContributorW5300 may be capable of 100Mbit/s, but is your system (NIOS+RAM+software+W5300) capable of that performance level? From your code snippet, I'm guessing the answer is no: running your IORD()'s should be a handful of clocks each (and I'm assuming they are in the same [fast] clock domain as the NIOS), so I am guessing all your time is being consumed within test_tcps().
Because you only need a modest improvement in performance over what you've got working already, I would suggest briefly reviewing https://www.altera.com/en_us/pdfs/literature/an/an391.pdf and picking one method you are comfortable with to find the biggest bottleneck in your test_tcps(), then just make whatever easy change to improve that bottleneck. To answer your original post, DMA really wouldn't buy you much in the above code snippet, as I think all your time is spent inside test_tcps() which DMA wouldn't help one bit.
