Yes cleaning did wanders on mine, I have the same card, 7800 GT
... and I just posted this the other day, here:
GX2 / Temps / Case Fans. Most of the post was to explain the reason why you should take out the card and air dust clean it, example of improvement is probably more of what you are looking for, hope you get more out of it after dusting.
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Proper way would be to take the Graphics Card out, or any other device you need to get dust out of. I just did the same with my computer, see I wasn't taking the Graphics Card out and blowing all the dust out of the cracks (or should I say, out of the holes, like the heatsink and fan. I seen a lot of dust bunnies fly out of it, just by doing one punch of that air
... So I hit it real good with several more blows, and lots more came out. So best thing to do, is take out the device you wish to dust blow, and keep the can upright, while tilting the card/device to where you need it. Be careful though, you might want to buy a wrist band that you can connect to the Computer Caseing, to keep the human body static from hurting your Graphics Card or any other device effected by Static Electricity.
Example of improvement: GeForce 7800 GT - Temperature I was getting without a good cleaning for I would say about 3 years, 67c - idle (I saw it peak past boiling point several times, while in play "couldn't play long "). I first cleaned my graphics card with just a Q-Tip (cause I couldn't find the straw to my air can), like took some dirt off the fan with the Q-Tip, it put my Temp to 57c - idle. I then finally found that straw to the air can, and blew out all that dust and dust wads from heatsink area and fan (basicly the whole card), now I'm getting 46c - idle, I had it peak to 77c today while playing a game. 100c is boiling point. So it's kicking like new again I hope your new card works great for you... what games do you play?
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Get to dusting,
Joshua Inman aka LuDawg