El Tigre said:
They will work fine, if one card is clocked faster than the other, the faster card will downclock to match the slower card. Just make sure your case has good airflow and your PSU can handle both cards and you should be good to go.
Actually one other question, what would be the safest way to install the drive if Windows 7 64 is already installed.
I was thinking to completely remove the nvidia drives/software, install the second card, boot up and then continue with a fresh install of the nvidia software.