Unfortunately, the CNPS 9900 is not a good performer on i7s, but it's not terrible either. If you have the money and case space, you might consider investing in something better. You can get them pretty cheap, such as the Core Contact Freezer
, though in that case you will need this extra bracket.
That being said, 70C is NOT an okay temperature while installing games (which is basically idle). If a reliable temperature program is telling you that your cores are near 70c while installing games, you have a problem and should not put any serious load on the processor until you fix it. If I recall correctly, Intel's specced max safe temp for i7s is 68C, and safe overclocks keep 100% load temps near or under 70c.