Something else to consider is where to put the fans if there's room in the case for multiple intake and exhaust fans. I find putting the intake near the bottom on the front and the exhaust as high as possible in the rear (i.e. right under the PSU) decreases internal case temperature by as much 2-3 degrees Celcius compared to the other possible arrangement at each location (i.e. 27 vs. 30 degrees in my Antec tower case on a typical summer's day). Keep your cables as far out of the way as possible, and that arrangement should give you decent airflow.
At the end of the day, there's no substitute for measuring it yourself under different configurations and system loads. Check with your mobo to see if it has temp monitoring software. Otherwise, try any of the commonly available status monitoring programs, like Speedfan, and give it a try yourself and see the difference.
