Hi there...
 
In my seeking of setting up a PC barely noiseless, I choose to change my video card, wich was a nVidia GT430 1gb for a Radeon 6450 1gb fanless... I was really impressed with how quiet my PC get, but I think it is compromising my PC performance... I have opened a song made when my nVidia was up and the system is flowing with less "fluidity", you know?
 
Is this possible?

I don't know anything about that particular card.
What kind of issues are you having with performance ?
My Nvidia Gforce 210 has been partly responsible for giving me lots of pops and crackles but their newest drivers seem to have resolved it for me so far.
There is a very useful free utility called Latencymon which measure your computers ability to handle real time audio and will tell you which drivers are playing badly.
 
Steve

What you don't want in a DAW is a high-end graphics adapter. They want to own your computer because they assume you're playing video games or doing high-resolution photo editing, where video performance trumps everything else. But video refreshes and smooth graphics aren't the most important thing in a DAW, moving audio data is. Don't worry about lost "performance". The performance is still there, it's just moved to more important tasks.

bitflipper
What you don't want in a DAW is a high-end graphics adapter. They want to own your computer because they assume you're playing video games or doing high-resolution photo editing, where video performance trumps everything else. But video refreshes and smooth graphics aren't the most important thing in a DAW, moving audio data is. Don't worry about lost "performance". The performance is still there, it's just moved to more important tasks.

Here I have to disagree with you Dave. Although I have never had a cutting edge graphics card I have in the past had very good ones. At present have a very mundane Geforce GTX 550 Ti. It has a fan and 1 GB of Gmem. The better the graphics card the better the better the over all performance. Also the Nvidia cards has CUDA processing. This can help greatly with processing when a program supports it. Vegas does. 
 
Plus now with Windows 8 and the very high res graphics a fast card is going to help. The notion that poor screen updates is acceptable because processing is going to the audio is only useful if you are not looking at the screen. Trying to read meters or any other analysis. If you have a plugin like Ozone 5 its crucial to have a snappy display.
 
To the OP because a card has a fan does not automatically mean unacceptable noise. 
 
 

yeah...but if there is any area where a DAW user/builder can skimp, is graphics. and there are a number of cases where the high-end cards do fight the audio/DAW for resources. not so much the case with Sonar but in Pro Tools, its self evident. alot of users have found better stability with some of the cheaper ATI Radeon cards, that avid does not recommend. 

I'm having a lot of graphics problems with X2 and one of the questions that Cake Support asked me is what card am I using.

nvidia GT640 2gigs of Ram.

They said the more modern the card the better. Mine apparently fits the bill. I also have two others, an Asus , and another Nvidia. Both much older cards. I have to say none of them work particularly well. Lots and lots of graphics issues.

Question, do you have Aero enabled with the new card? It's best to leave that on so that the graphics get off-loaded to the card and not your CPU.