In terms of graphics card the really important thing to know is what resolution you are planning running. I'm guessing 1920x1080 since your monitor is 24"? In that case the GTX 760 will handle pretty much anything you throw at it, the GTX 750ti is still a strong card if you aren't planning on playing AAA titles on Ultra.
In terms of cooling/temps, it's more about the vendor you go with as they normally build their cooling from the ground up that are much better then the reference models. It really is worth spending a little bit more now for the same card from a brand with a good reputation (ASUS, Gigabyte, MSI etc). Also check the stock clocks, some cards run slightly faster out the box then others.