I was planning on using two separate outlets on different breakers thats not a problem running the numbers honestly running an SP30 at 4.1 TH at 2600WATT actually
running the numbers provides a better hash/Watt number than 4.5 TH at 2900WATT, not sure what all the big deal with maxizing the hash ratio to all ends is. Hash/Watt
is what matters in the end.
If you already have 2 circuits installed, then just buy the cables with the correct ends, and you should be good to go. Honestly though, even at 3kW, you're not to go over 12-13A @240v, which is perfectly safe on a 20A circuit.
Find the plug that matches your recepticles:
http://smile.amazon.com/SF-Cable-NEMA-L6-20P-250V/dp/B009ZERV72http://smile.amazon.com/6-20P-Power-Cord-Adapter-Foot/dp/B00H7JR636/This one already has 2xC13, so you'd be good to go.
http://smile.amazon.com/L6-30P-C13-Splitter-Power-Cable/dp/B00BGAEBNU/And of course you can easily get C13-C14 extension cables wherever (online...Don't expect to find them at Ace Hardware). Though I would be sure to get those cables rated for 250v & at least 15-20A.
As to the W/Hash ratio, that is what matters "in the end" only so much as you are talking end of life of your hardware. As RoadStress said after the difficulty is >70B. Until then, maximize your hash rate as much as you safely can.