I'm not sure I follow exactly on the setup you are running but it sounds awesome and similar to what I had plans to try next if the amp draw lived up to my expectations shown on paper. Any pics of your power setup? Would love to take a look if you get a chance 
I had a thread a while back with some photos not sure if I can still find a link.
Essentially NEMA 6-30 is just a 30A version of the plug you have. They make a locking connector version (L6-30A) which you insert and turn to lock. Nice so a cable pulling 30 amps doesn't get knocked loose.
If you ever need a lot of power the cheapest (and safest) setup is
1) put in a new 30A breaker in breaker panel
2) run a line to a new L6-30A outlet http://imageserver.grainger.com/is/image/Grainger/1PKK1_AS01?$productdetail$
3) Grab an AP9571 made by APC. It is a PDU (power distribution unit) which is a fancy name for rack mounted expensive power strip.
Any PDU will work but the nice thing is APC made like a quadrillion of these in the last 20 years so used ones are always available on ebay for like $30 to $50.
http://www.ebay.com/itm/APC-AP9571-Rackmount-PDU-12-port-Power-Strip-208V-24A-/231025800012?pt=US_Power_Distribution_Units&hash=item35ca35f34c
You will notice the plug on the end is NEMA L6-30P. The cable is like a firehouse. Never cut one open but it has been to 8 gauge are larger cable and surrounded by good 1/4" of insulation. 230V * 30A * 80% = 5.5 KW and it comes with 12 C13 outlets. You can run a whole ASIC farm off one or two of these, although it wouldn't work with that 1600W PSU.