Form late 2009 i7 imac to?

Hey guys,

Long time youtube subscriber, first time poster.

Before I start, I know that I am one of thousands that post up possible system builds, but any advise would be much appreciated.

Im a building surveyor, but work as a store planner, architectural technician/visualiser & graphic designer in the UK. So I use autocad, sketchup, illustrator and photoshop every day for around 8-10 hours. As for sketchup, I use both indigo rt and twilight for rendering, I'm also starting to use lumen rt more for walk throughs.

Currently I'm using a late 2009 27" i7 imac with 32GB of ram recently fitted with a SSD for the majority of my work. External storage is handled by a 4TB NAS. 

I had played with the idea of buying a 6 core Mac Pro, but my experience with sketchup 13/14 on osx hasn't be great so for that and other reasons I'm now thinking of moving back to windows (7, not 8).

So I'm looking at building a new machine. Here's the parts list as it stands now.

Intel Core i7 4930K - £419.99
Asus P9X79 Socket 2011 8 Channel Audio ATX - £191.99
R9X/780ti/AMD FirePro V7900
Kingston 240GB HyperX 3K SSD - £139.98
WD 1TB Black Hard Drive - £58.73
Corsair 16GB DDR3 2133Mhz Vengeance Pro Kit - £139.98
Corsair Hydro Series H110 280mm High Performance Liquid CPU Cooler - £89.99
Corsair Professional AX860 Fully Modular 80 PLUS Platinum 860W PSU - £142.98
Corsair Carbide Series Air 540 High Airflow ATX Cube Case - £116.98


- The long and sort of it -

Gpu - this is where I could do with some real advice, particularly from anyone who uses similar/same rendering software. I had been thinking of an R9X or the obligatory 780ti, as a work station card is a little pricey. Also a reasonably priced fire pro is only going to provide 2GB.

Budget - reasonably movable here, but I'm not after paying stupid monies for the extra 1-5%, but I don't won't to feel like I need to upgrade by this time next year. So if there are any parts above that have more price competitively counterparts it be happy to hear.

Well, thanks for making your way through, any thoughts or advice would be very much appreciated.

P.s. I'm not planning on play any games at all, I have the peripherals covered and I'm looking for stability not over clocking.

Thanks!

Thanks for the reply Kai,

i'v been running windows via VM fusion for some time now. Plus I have a HP workstation, and SU works very stably.

I'm still undecided as to what direction to go. Mac Pro or build a work station.

Any my advice or recommendations would be much appreciated.

thanks all!