I have a similar question. My case comes with a 120mm rear fan with possible expansions of 1 side fan (120mm), 1 front fan (120mm), and 2 top fans (120/140mm). Would the rear exhaust fan and a front intake fan be enough for a non-OC'd Sandy Bridge with stock cooler and a non-OC'd 6870 GPU with dual fans on the card? Micro ATX case form factor, standard bottom power supply layout. Please let me know from a a)component safety perspective and b)a low noise perspective.
As far as noise goes wait and see how the system sounds. Since it seems like you've already ordered the main components there's no point in spending money now that may have no noticeable affect on noise levels. If you do have an issue with noise open up the case and start replacing things based on whatever makes the most sound. Chances are the stock CPU cooler will probably be the first to go. Since you're not overclocking anything you won't have to worry about temperatures at all. As far as case fans go it depends on what case you have, some are garbage, some are decent.
Ok, I will get two to replace stock H100's fans. Do you recommend replacing stock CM 690 II's fans? If so, which ones do you recommend for air flow?
The 690II fans are fairly quiet. With the stock fans the loudest thing in my PC is the GTX 670 fans (Which are pretty damn quiet) and HDD seeking. I haven't started to seriously overclock yet until I'm sure all my components are stable and working properly at stock. So far temps are fairly good in the case. With Kepler and Ivy bridge running at stock nothing in the case really creates much heat in the first place