I was wondering this myself. I think the base SLI has only one ethernet connector and 4 SATA connectors, and perhaps limited onboard I/O connections.
The premium has 2 netword adapters, 8 SATA connectors, and the full entourage of I/O
The deluxe has everything the premium has but includes special heatpipe cooling for the chipset.
I think ultimately, they are all the same board with the same chipset and same construction quality. The base SLI is just a reduced version. Have fun.