An ordinary geforce really ought to be enough, even since years ago it's been considered gaming cards are up to the task whereas quadros, firegl are more justified for CAD and engineering types of software.
The HP Z1 looks marvelous for sure, and is an interesting cross between a laptop and desktop but the cheapest and most flexible solution has to be a micro ATX tower (if you can afford the PC to take some room but not be huge)
You can get a GTX 660 2GB, it's a vid card that doesn't heat too much but still is very powerful, else if you expect to do GPGPU rendering of complex scenes and can afford it maybe a GTX 670 4GB.
With a low budget, and partly for the lulz an MSI N640-4GD3 4 GB may be considered, it has a lot of vid ram for playing with (for experimenting with stuff that needs a lot of vid ram) but it's much slower than alternatives including a GTX 650 at a same or similar price. But it's low power and similar to a GT-650M, to draw a parallel with laptop hardware. Funnily it shoulld be around the performance, or higher, of the Quadro 1000M (but without the Quadro's software-specific driver optimisation, which makes it run smoother somewhat)
A high end Quadro may still have some uses for 3D creation, high geometry performance for displaying extremely high amounts of polygon but that may be not terribly relevant, it's for doing really high end stuff and when artist's wages cost a ton more than the card.