If you mean their graphical capability, in terms of what features they support, rather than performance, then you most likely want to look at demos of the different graphics engine versions, rather than cards themselves. For example, a card that supports only DirectX 9 will not have the same visual capabilities as a card that support DirectX 10. Two cards that support DirectX 10.1 should theoretically produce identical graphics when playing a DirectX 10.1 game. There are occasionally bugs in the drivers that cause artifacts, or other quality issues that create problems. There are also user controlled driver settings that can change how the game renders, but the point being that the capabilities are that defined by the DirectX standard that the card supports.
As part of the card's specifications, it will list the DirectX version, as well as the OpenGL version it supports. This is the main specification that differentiates one cards graphical capabilities from another. There are some proprietary capabilities, but I would guess most game developers don't use these, as it would mean their effort in implementing those features would only be seen on certain video cards.
Here's one I've seen used before, links for installer are on this page:
http://www.unigine.com/download/
I have that exact same card, and the only game that has performance problems on the highest settings is Crysis, but that's a given. Other than that, go ahead and ramp up your video settings to full. (I also have a pretty powerful processor, which may or may not be the case for you.) – Sasha Chedygov – 2009-08-15T19:35:58.813
CPU will be Core 2 Duo E7500, but I don't want to continue game machines topic, as it usually never ends itself :-) – Tomek Z. – 2009-08-15T21:00:10.203