The MSI has a slightly better clock speed but apart from that they are pretty much the same card. The only other obvious feature is that the Gigabyte has 3 cooling fans where as the MSI only has two but to be honest, that won't make a difference when it comes to performance. and yes the is a bit cooler, but then again it depends on ur system.
If u have a good system with good air flow then u wont need to worry about overnighting problems.
I have the msi gtx 760 twin frozr oc 2gb and i get amazing performance and low temp around 26c when doing nothing and when i game at worst it goes up to 45c. The gpu can handle up to 90c before crashing.