You can SLI it... but if there is a problem with the card, it would cause problems in the SLI setup as well. A single different card is also a good option.
The best one is... stick with the pain for a little while longer and let the HD7xxx cards come out in December, weigh your options then and get one.
I am in no hurry to get a new card. Have ordered a few case fans to improve the airflow, hope that helps some. How much would the HD7XXX series cost approx. when it's launched? and will it bottleneck my setup?