AFAIK a Deneb does not work in DMA mode in a 3000 with onboard SCSI, regardless of Buster rev.
IMHO 100 or 10 Mbps Ethernet doesn't make too much of a difference, given the overall bus speed of a 3000 (some 11 MB/s).
A Deneb is an extremely versatile solution that offers a lot more than just cheap Ethernet - for a price.
I've got an A2065 Ethernet board (~$30 two years ago) and a generic twisted pair transceiver ($5) to avoid the cheapernet connector. Also got a PCI board (Prometheus) which I never got around to install and which would run a cheap/free 8029 PCI card.
