I've had no cooling issues with either of the installed 9800s. However, the card which is closer to the NB runs a little hotter. These cards fans offer plenty of cooling and when the fans are spun up to 75-80% its loud.... One interesting issue with my cards is once they spin up the stay at that speed until I reboot. I installed Riva Tuner and now use custom profiles to manage my fan speeds.
I have two Gts 250's on my P5N-D, only issue is the SATA connectors are in the way, four are provided and two are useable with SLI with my Cards