The heat inside your case will not see a major impact if you opt for the reference model GTX 580's in SLI. The vapor chamber coolers will vent all heat outside the case. The GTX 590 will vent about half the heat outside the case, while custom GTX 580's will dump all of their heat inside the case.
All the same, all of these are common setups and you have a good case with good airflow so system temps should be well within normal operating limits regardless of which option you prefer. The SLI option will be faster with better heat management, but will cost considerably more. The GTX 590 is often the choice of those who are unable to do SLI with two cards.
That would be the 3rd time in 2 days you incorrectly assumed something that was clearly stated otherwise. I suggest you read each post at least 5 times before you reply in the future because your reading comprehension is seriously lacking.