As you stated you already know the answer. Sorry, once you start to drag older devices/items along, sooner or later something is bound to cave. You will be in some repair cycle replacing this or that, though it could be done as such. While the video card is capable as well as the PC overall, if this constantly powered-ON it will start to overheat if NOT cooled well even with basic PC case cooling. On top of that its already X-yrs. old and that can't be good, you already got good service out of it, this is waiting to falter. I suggest you find a newer PC or build one and add the recent video card and 1Tb HD to it and start from that. Otherwise, just get a new PC and the cost for even an entry level PC is reasonable once you consider the costs of build or upgrades of an old one. Going the extra $ to get new is worth it. In most cases, you can remove the 1Tb HD inside the ext. case and often enough the HD is OK. I suggest you look at either another ext. USB case or "dock" for ease of re-use.

tada -----Willy Happy