Some responses with this kind of question tend to be along the lines of 'get the biggest, baddest thing possible' - it's common sense that a faster computer will compute faster - but as someone who doesn't live where money grows on trees, I like to consider just what I really do need to get the job done rather than going overkill on hardware I won't actually derive much benefit from. You do not need a computer with a processor that costs $800+ alone to make great animations with great visuals. Unless you are doing Weta Digital levels of rendering insanity you'll be fine with a reasonably powered quad core (or more) processor, a mid-to-high-range graphics card, and 12 GB or greater RAM. The faster your processor, the shorter the render times will be; no surprise there. You don't need to overclock things only to have them fail sooner because of it and cost you more money.
If an expensive rig finishes a multi-thousand frame render job at 3am and a rig less powerful finishes at 6am, but you don't wake up until 8am anyway, it's worth considering just how much benefit you're experiencing for potentially paying significantly more more for the computer.
I'm currently on an i7 1.6Ghz laptop (4 physical / 8 virtual cores) with a mid-low range graphics card and 12 GB of RAM, which in total cost about $1,200 in 2010, and I'd be just fine with it if I was still into traditional offline-rendering 3D work. It takes about 6-10 seconds to do preview-level renders complete with GI. None of this hardware is very remarkable at all, but it's entirely capable of pushing pretty pixels, so when I see the 'make a supercomputer' posts that often pop up in this kind of thread I can't help but imagine they are being written by men in limousines throwing money out of their windows while typing.
And works on non-'professional' computers just fine. But I'm sure someone would love if you spent way more money and bought a Quadro card which, at least in the past, was the only 'officially supported' graphics card series for Max despite that it was somewhat of a joke and GeForce worked fine.
If you're making money off your work Quadros are worth every penny. Dedicated drivers, reliability, dedicated support and access to nvidia's driver devs, thoroughly tested and guaranteed compatibility through ISV certification programs...
Hence the single quotes on 'professional', it's a term used a lot on workstations that seems to suggest magic, but they do tend to have Quadro or FirePro cards. I've known quite a few people who make money using Max/Maya, none that have voiced it have had Quadros or have shown any interest/need for the extra support and certifications that may come with it, as their consumer-grade cards have done perfectly fine in getting the work done.
The original point being that Max works fine on 'gaming computers' that have reasonably fast components versus workstations that can cost 5 times as much. It's what our school's computers essentially were: gaming computers - no workstation video cards, ECC RAM or other fancy bits that would separate them from good machines to build if you wanted to play games, and it's not that we were being light on them as 30M+ point ZBrush models and the maps to match them were common. We did have a render farm, but not many seemed to use it. The average person who is not working at Weta Digital, in my opinion, is not going to require that last stretch of performance increase that adds another 50-100% or more in cost.
If you've got big clients and are dealing with big money, those costs may be trivial; those accumulated saved rendering hours invaluable. For many others, especially someone who is asking online for recommendations (especially on dA), they can save a big chunk of money and still do everything they intend to by realizing that yes, Max is an industry standard program, but it does not require a black monolith powered by cold fusion to use effectively. How pretty the pixels are that come out is much more in the hands of you as the artist than in the hands of that photon count slider you jacked up for your computer to sit and think about. It's very easy to buy something that you'll not benefit greatly from; very easy to spend more money than you really need to.
By no means am I saying that there is no benefit in having a completely loaded workstation; only that it is entirely possible to create great work without one, and it doesn't mean that it will be a pain to do so.
CPU: 3930k Cooler: Noctua D14 Motherboard: ASUS P9X79 Pro RAM: G.Skill 4*4Gb 1600 CL9 GPU: GTX 660Ti Case: NZXT Phantom PSU: Antec Earthwatts EA750 OS: Win7 Pro 64bit
(OS defaults to Win7 Home Premium which has a 16GB memory limitation, upgrade to Win7 Pro 64bit, or if OS is not needed select none and pocket the difference or add an ssd boot drive.)
Total: $2043 with Win7 Pro listed configuration / $1943 as listed with no OS or $2007 as listed with no OS with the addition of the 128GB Crucial M4 as boot and Seagate Barracuda 2TB secondary storage drive.
It's been a while since I looked into 3D rendering, but what are the impacts of memory bandwidth on programs like 3DS Max? The GTX 660 Ti is rather anemic in that department (that and ROPs, but I'm pretty sure those aren't used much in 3D rendering),
There'd be some benefit going to 1866 or higher, tho those G.Skills will happily do 2200Mhz.
As for the graphics card, ROPs don't matter as much for compute. Vram bandwidth, compared to what? For a render, 2GB at 140k MB/s of bandwidth should perform around the same as a 570, better even given it has more memory. 670 wouldn't be much better at compute given same amount of shaders and same clocks, bandwidth advantage with the larger bus is marginal at best.
If you look at it from a gaming point of view, the 7970 has around 30% more memory bandwidth than the 680. Clock for clock they perform around the same in most games, with the 7970 being maybe 3frames better at high resolutions/vram limited games. On a render, that probably translates into mere milliseconds.
Of course, a 3GB 580 or 4GB 680 would be best, I doubt it'd be worth the extra cash tho.