4GB sounds about right for the 6500. I actually was able to install a PCI USB card into my 6400 and run a Microtek USB scanner and a Lexmark laser printer on it on Mac OS 8 (can't remember if it was 8.1 or 8.5). I also was able to install an upgraded video card in the other PCI slot and replace the GeoPort (?) modem with a 10-base-t ethernet adapter to connect to a cablemodem. Managed to make that machine last until 1999 when I replaced it with a G4/400 (before they downgraded those to 350).I had a Power Mac 6500 with 4GB, but, granted, that thing had some bizarre upgrades in it, including a USB 1.0 port. So I can’t guarantee the 4GB hard drive was stock. (I’m assuming the USB port was added a couple years after the fact for software authentication dongles, after USB had become common. Since it had previously been used in a music education environment, the idea of authentication dongles doesn’t seem too far fetched to me.)
Man. Good times.