Definitely keep the 5400 - its a black 5400, and they're very hard to come by these days, especially in good condition, with the matching black keyboard and mouse. You can pick up another 6500 one day whenever you feel like it, they're still fairly common, and since you've got the 300 Mhz board in the 5400, there's nothing that the 6500 really has to offer that the 5400 doesn't, apart from a tower enclosure, one extra PCI slot, and the subwoofer. So yeah, keep the 5400.