I've been trying to resist, but I've got to chime in here.....
First, The approach of dumping conditioned air into an attic should only be used if you have no other option in my opinion. Aside from being inefficient from dumping air (that you paid to condition) outside, it also has the effect of creating a slight negative pressure situation in your home which means that it pulls make up air from the outside through any spot in your home that it can. Unlike a bathroom or kitchen where you also need to be rid of humidity, smell and smoke....an electronic equipment room doesn't have those issues. Every piece of equipment is designed to run in standard ambient temperatures. All you are looking to do is keep the equipment room at an ambient temperature of 85-90 degrees or less. Draw conditioned air into your equipment room and dispose of it back into the conditioned space through a standard vent far enough away that you don't short-circuit the ventilation intake with the warm output.
Second, use a variable speed
thermostatically controlled fan. With the options presented above, the fan is either 100% on or 100% off. A variable speed thermostatically controlled fan operates only as much as it needs to and is therefore the quietest possible solution. Additionally, if you use these higher CFM Fantech fans, be prepared for your equipment and equipment room to be filled with dust at a much more rapid pace. That Fantech fan is 263 CFM, which is enough capacity to handle FOUR - FIVE full-fledged bathrooms, let alone a small equipment room with some electronic gear.
Third, I would look at professional solutions to simplify your life and provide a thoroughly engineered system for about the same money or just a slight premium over cobbling all of these parts and pieces together into a DIY system. Here are some examples:
Middle Atlantic Closet Cooler or Duct Cooler: http://www.middleatlantic.com/rackac/cooling/qcool.htm
$284 for closet cool system, just over $400 for the complete duct cool system, fyi.
You'll notice that the MAX CFM for the closet cool system....specifically designed to force ventilate an entire rack of equipment in a closet.....is just 50 CFM. Most of the time your CFM cooling needs will be MUCH lower. The built-in thermostatic controls will minimize noise, limit the amount of dust being passed through the room, and will only operate to the necessary speed. I personally have TWO full-height 44u Middle Atlantic Racks that will be filled with high-powered equipment, including 9 amplifiers in an equipment room that measures 4'x9'x9'. Even with all of this equipment and the BTUs generated, I've calculated that I need and absolute max of 105 CFM, but most of the time I won't be running anywhere near that.
Food for thought. Good luck!