Jeff if your serious about security camera get yourself a proper DVR either custom chipped or linux / windows based one which has the correct hardware and software codecs etc running on it..
I know what I'm on about as well, given I've spec'd quite a few up for customers. Some capture cards are okay some are flaky as heck but watch out for "Geovision" cards unless they are bought from GeoVision themselves or a registered GeoVison reseller don't buy - no come back with them and no support from GeoVision.. Just a heads up.. I've used windows / linux based DVR's quite good actually what you can achieve.. although if these are static / short term then it maybe a but OTT... Most come with software that lets you remote view or a webpage that does the same, some do both, and some better than others.
It's not always the "fps" but the raw processing power needed to recode the images for transmission as you think about it take a 480x320 (2-CIF) as it's known that's 460,800 bytes of data (assuming 24-bit color) per frame or 11,520,000 bytes per second that need coded to be transmitted say via x.264 or mjpeg that's a lot to do and some capture cards can do it providing they have the CPU behind them..