Rendering, like full out rendering, is taxing and limited by cpu, graphics, memory, storage speeds, and graphics cards.
Memory is what limits the cpu. Cpu is the workhorse in rendering. Graphics cards accelerate the rendering process, but its still heavily based on the cpu.
While rendering, the speed of writing is actually what determined my bottleneck. I had beast setup, and cpu was at 44% (ish), and graphics was only minimal. I couldn't figure it out, until I saw that my hhd was at 100% with 140mbps. I hooked up two in raid, same story except more cpu and graphics % usage. But still raid hhd was 100% at 250mbps. Switched to solid state, and it was around same story, except everything was all over the place % usage wise. cpu was 20% then 80%, then 60%, then 20%. same with graphics, until I realized that ssd usage was fluctuating between 100mbps to 500mbps. Also found that the limit for speed, includes both read and write. If its 500mbps, and your reading and writing to same drive, its like 200 mbps read 300mbps write. But if you read from and write to a separate drive, then your at each drives max, so if both drives 500mbps max, then 500 read/500write is possible. I found that 400-500mbps is around the minimum it takes to releave the storage speeds bottleneck while rendering, and led to a constant 100% (well like 98%) cpu usage while rendering.
Using ram or separate ssd for a scratch disk, doesn't apply to rendering times, but every time you change the original file, without actually finalizing/rendering, it gets saved to this scratch disk. Traditional hhd scratch disk took about 10 seconds. So any time I would click apply for anything (like adding effect, or anything of that sort) took about 10 seconds (circle spinning system unresponsive) before it would finish and I could then continue working. Solid state for scratch disk moved that delay down to about 1-2 seconds. Ram, that pause was non existant.
For graphics, I say use workstation, as it seems that's what this build is going to be. And workstation class gives pure drivers that are 100% utlilized by your programs. And single best you can afford, as a lot of times when you sli graphics, your not getting 100% of both, you actually loose a lot. And ive found from my sli titans, that while theyre working together, they don't work 100% in unison, and actually ends up throwing off your final product a bit. Plus your heat, noise, and required power are all also lower.
I chose the asus deluxe, as it offers exceptional 'goodies' that are aimed at making the most of a rendering build. The rampage black that I chose is $200 more, and offers more 'goodies'. That switch is up to you, as final rendering will be identical between the two boards.
Corsair dominator pro/platinum 1866mhz ram, gives you great performance, xmp profile in motherboard bios will fully utilize the ram. They use the best chips in their ram, which means less problems down the road.
I say evga and seasonic as they are the top two, corsair and xfx also make some top quality products. I have the evga supernova, and its great, fully modular, great efficiency, and a 10 year warranty.
I say Western digital blacks, as theyre top notch best in class. More expensive, but its worth it over loosing everything you have stored when a cheaper drive goes crap. 5x in 9 months for my seagates.
Case, its more personal preference. You want something good, big enough to house everything, give great airflow, built in dust filters is a must in my book.
I chose corsair 540 air, as it is essentially a full size case, but instead of being a tall tower, its like a box. All the hot stuff on one side with all the fans, and all the cooler stuff on the other, makes cable running easy and tidy as well.