I have replaced the fan in mine with something smaller and quieter. The Q950 now emits a low growl that is much more satisfying to the ear than the original racket, and quite in keeping with the character of the machine. It'd rate it as one of the quieter machine in my collection, in fact. As part of the modification, I removed three spare nubus covers to allow for enhanced air circulation from the nubus slots area at the rear, across the nubus and pds cards and processor, around to the fan at the front, and then out the back via the exhaust system. Works a treat. With this setup, and even with a much smaller fan, I have no resulting heat problems, and no noise to speak of. I have run it this way for weeks at a time.
So I'd highly recommend a transplant — assuming that the cards and so forth that you have installed do not normally run hot. You'd need to monitor it for the first little while to ensure that the machine does not overheat, but all should be well.
I'd bolt a replacement fan to the wire cage over the original fan area, ideally with rubber washers to reduce vibration, and modify the wiring to accommodate the new fan (or connect it to one of the spare drive power plugs). If you plan to use the machine much, you'll not regret the small trouble taken.