Graphic card

Im very confused right now, i need a new graphic card and i cant understand the differens between quadro and plain geforce.
im using ironcad ver 9 and everything i find on the web is for older cards and so on.
Im working with scenes above 50mb and been told that quadro is the way to go.

Is there any other cad cards around?
is a quadrocard really better than 2 plain ones in a sli config if you have 2 plain cards for the price of one quadro?