According to this they would be mediocre at mining - potentially less than today's $100 ATI cards each
https://en.bitcoin.it/wiki/Mining_Hardware_Comparison#Nvidia


Also https://bitcointalk.org/index.php?topic=4404.0

Quadra 6000 are 3 year old cards.  They probably still rock for other things, just not for the type of calculations that mining is.