32-bit 33 MHz PCI theoretical total bandwidth is 133 MB/s. Realistically you won't get a single card to pump more than 100 through - and that's already blocking out everything else.
TV capture stream, soundcards or anything like this is nowhere near problematic. The one thing that will hit the ceiling for sure is high performance mass storage controllers - SATA RAID, or (even single-drive) SCSI.