I would take eVGA they is better company and better cover in guarantee
What does that mean? MSI is a great company, they make many things from mobos to desktops. The hawk is by far the better choice once OC'd, the difference from heat inside all depends on your case airflow. If it is garbage with no intake fan, then your bound to get your entire computer heated up. I'd recommend at least having one 120mm fan for intake. AT LEAST. And at least 1 or 2 120mm fans for pushing out the hot air. The exhausting air with out good airflow would probably stay inside the case for a bit before getting pushed out (hot air flows up) or by a fan. But that will be after it heats up your CPU and other things like that. The Air exhausting outside is decent but is minimal to the amount that should get exausted into the case. So good airflow is key for both cards.
I might be wrong though, so correct me =P
I recommend the Hawk 460 though for it's OCing cabability and ability to keep WAYYY low temps under load while in decent airflow.http://www.techpowerup.com/reviews/MSI/GTX_460_HAWK/31.html
The review below should tell you (possibly) that the EVGA 460 will run hotter than the Hawk after OC. http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/34207-evga-gtx-460-768mb-superclocked-single-sli-review-19.html