Phenom,
I'm going to try to explain this to you as best as I can, so please take my rant as informational, and nothing personal.
The reason Quadro cards are a bad choice for playing games on is simply because that is not what they are intended to do. They may seem like a good idea, because they can have similar (or nearly identicle) architecture, but with lots more ram...but they are designed for things like graphic design, where large images are being produced and edited.
The drivers for these cards make them operate to perform best in this area, which is almost the exact opposite of how you'd want a graphics oriented driver to act. In a game, you want the card to draw a picture quickly, and send it out quickly. With business oriented quadro cards, you want a detailed picture drawn very precisely, which takes more time and resources (this would result in lower frame rates!).
Additionally, the way GPUs work (and most computer stuff in general), you have brand new architectures released every 2-3 years that revolutionizes the industry. Looking to the past, you wouldn't be able to play any modern games on a card from 10 years ago. Even if it were the best available at the time!
For example: the 3dfx Voodoo 5 6000 was released around 2000-2001. It had 128mb of Video ram, used the 4x AGP interface, supported 8x AA, and DirectX 7! Even IF you were able to SLI them (a technology not available at that time), With directX 9.0c being released in 2004, the VD5 would not support a game made after 2005-2006...and that's a lenient estimate.
So flash forward now...if you got a card today, quadro or mainstream GTX...ten years from now you'd have
A. a nice paperweight/conversation piece, or
B. still be playing games that came out in the early 2010's
because: you buy a gtx 580(for example) today. in 3 years you SLI a 2nd, 6 years a 3rd. In 6 years, games will be designed using probably Direct X 13, which your cards would not support at all. A new interface will probably be available, so if youd be stuck on an old motherboard to maintain compatability, and this is assuming you could find a GTX 580 in 3 or 6 years! I had dual 8800GTXs in SLI back in 2007-08. In '09 I could no longer find one outside of Ebay at a rediculous price.
It may not be the easiest thing to understand, but please take the word of the folks on this thread that a quadro card is a bad idea because it is not designed to play video games. Also, whatever you get will NOT last you 10 years unless you are intending to spend the next 10 years playing games that are built on DX11. There are a lot of options out right now, as the the current generation is comming to a close with the release of Nvidia/AMD crowning achievement dual-gpu monsters is near. If you are single monitor gaming, you can get a great card to last you 2-3 years for $300 or less. I hope this helps you in some way, even if just a little bit!