I have the noctua NH-U9BSE and am happy with it. Don't know too much about the Ultima 90. As I understand it, the main advantages of the Noctua are that it comes with 2 fans so you don't have to buy them separately (which apparently doesn't matter for you) and it has "quieting" resisters that you can install to lower your fan speed to reduce noise. Performance-wise, it's worked fine for me on a I5-750 overclocked to about 3.2 mhz and I rarely break 50 degrees. I doubt it would be worth the upgrade unless you wanted a quieter fan(s).