CUDA on Geforce640 works with 304xx drivers, not with default version

Is this normal? As far as I understand the nvidia naming scheme, the 600 series comes _after_ the 8 series so I shouldn't be using the legacy drivers. However, if I try to run cuda programs with the up-to-data ones they all fail to find the device. Anyone else have any experience with this? Running Fedora 19, 64 bits Thanks, Michael