My bad, I meant to compare the one you originally posted (MSX6036F-1BRS) to the standard depth, 2PSU version (they are much easier to find these days)http://www.mellanox.com/related-docs/prod_ib_switch_systems/PB_SX6036.pdf
So different speed...
The 2 psu unit will use more power due to the second psu and its fan.
Cables- i also use DACs and found that with 40g IB cables you might fall down to 10g ETH.
FDR cables are not that expensive though, but didnt look for optics tbh.