There were so many bottlenecks and "issues."
Let's take note "that ram is 544 SDRAM and EDO" brings up a design limitation in chipsets that hosted the i233mmx. Depending on the chipset and board, the L2 CACHED memory space was 64, 128, or 256 MB of memory. I think I saw a few boards that did 512MB, but you've gone past that.
What upset some was they discovered Windows ran in the high memory which in these machines was uncached by the L2 memory. You may want to rerun your benchmarks with exactly 128, 256 and exactly 512 MB. I gave away the office AMD K6-400 machines with exactly 128MB and so far a few have called back to ask why they run slower with more RAM. What's interesting is that not only did I put a note with the machines about this effect, but I even told them when they picked up the machine...
Anyhow, the other issue that I find is that many will not load the motherboard drivers. In your posts, you didn't reveal the make/model of things and now we are conversing about a machine you can't give away. Get over it that it's a dumpster model and I know too much about that era and will help you a little, but you have to help the forum by spilling the beans.
Bob