First off there is no such thing as a Nvidia 2600 HD, it is actually a ATI (now AMD) Raedon 2600. Second this was release 7 years ago, taking the fact the slot itself it was made for isn't even used any more (PCI Express vs PCI Express 3.0) so it wouldn't even physically fit IN a slot, with a multi-core design and Dual Channel memory, this card would SERIOUSLY choke the system as it would be unable to handle the loading of code. Further this card was only rated for performance in making HTPC (Home Entertainment PCs used to stream / display video / audio, not gaming NOR CAD rendering)/
Anyone doing CAD type work (different rendering then video games) gets a WorkStation class video card, like the NVidia Quadro. The reason / point is usually in the time it takes to render multiple level in a CAD design for anything less then Workstation class cards can take HOURS to do then in minutes (as expected for the past few years). And forget a 'normal' CAD design (i.e. electrical, water piping, etc. plans for a whole building) it would 'crash' under the load.
NUMEROUS threads are searchable here with whole builds picked out, still comes down to a Normal 'Professional' Workstation (I.e. what is expected to do the job in the business field) STARTS at $2500 and just goes up from there.