Cheers, that is interesting. I'd only be choosing between an X520-DA2 (which I actually already have) and an X710-DA2 - it'll be fibre either way. Looks like the X710 only uses about 60% of the power of the X520 (5 Gbps/watt vs 3 Gbps/watt). Both 2 port, so directly comparable in this graph. That's actually quite significant.