Hey zachary,
I recently had a similar question. What i've learned is that a GTX 670 (or whatever) wont always give the best viewport performance in 3DSmax (or 3d modeling software) as compared to a quadro. But for gaming, and affordability, GTX series are great. The GPU doesnt weigh in on rendering for 3DS unless you're using an RT engine, like vray.
So, if you want high performance for rendering, i'd recommend getting a i7-3930k, which will give you 6 cores (12 threads), where 3770k is 4/8 core/threads. Now, not ALL software utilizes your threads, but i do know that vray is one of them that does. I'd assume mental ray as well. (refer to buckets in your rendering window).
Another note that i've learned is that a quadro is best for viewport performance and not much else. So much so that a lot of games can be unplayable. So, finding the right GTX is probably your best bet. Additionally, Adobe programs (AE CS6, Premiere Pro, etc..) all take advantage of CUDA technology for GPU rendering (SIGNIFICANTLY FASTER!!!!!) as opposed to CPU (or openCL).
I dont believe that Radeon has CUDA, which might mean that you cant take advantage of the GPU for exporting in AE/Premiere etc.. (but dont hold me to it)
Here are a few links:
http://forums.creativecow.net/thread/2/1019120 -- benchmark test for video cards -- some links showing performance of video cards, new isnt always better! (my GTX 570 completed the benchmark in ~6min 3sec)
http://www.studio1productions.com/Articles/AfterEffects.htm -- in the third paragraph of text there is a blue link that says 'Note 1' you can click that to see what GPUs adobe deems compatible, but if you have CUDA technology you can force it to recognize it by following some steps on the link
http://www.tomshardware.com/answers/id-1735788/1st-gen-haswell-rendering.html -- this is the thread that i posted when deciding my new CPU, unless you get the 3960X or 3970X, OR wait for Ivy Bridge-E (4930K) then you'll be spending upward $1000 for the CPU, and so i've concluded that a $569 3930K is the best bang for my buck -- especially when upgrading from a first gen 4 core 8 thread i7.
This is getting long, and you can stop reading here, but here are a couple upgrade decisions i plan to follow through with soon.
http://img.photobucket.com/albums/v106/howdybillybobjoe/upgrades.jpg
I plan to overclock it (since i will primarily be using it for rendering) and so i will also be watercooling my system, which i would recommend if you're going to put a lot of strain on your CPU (or GPU, too). However, i'm far from being an expert on that, so youtube or Tom's forums will be your best source for help on that.
Goodluck!