Well, the card you just linked us to has a decent performance.
Would be able to play Doom 3 (high settings with AA) at 44 fps for example.
Go here:
www.tomshardware.com
Click on charts, select Desktop charts, then scroll down and have it display ALL cards.
Then select a desired benchmark test from the list (whether a program or a game) and it will display just how well the 8600 GT performs.
As I said, Doom 3 should be able to play nicely at high settings (I extracted the info from tomshardware site).
So given the price/performance ratio ... yes I would say it's a rather good card.
However, it is questionable if your power supply would be enough for that graphics card.
You might want to take a look into buying a 400 W (minimum) power supply