Hey Darksim! Well first of all,a link about performance in nvidia and amd cards,it´s for the profesional line of gpu´s,but maybe you´re curious about what card has better performance in determined programs:
http://www.cgchannel.com/2013/11/group-test-amd-and-nvidia-professional-gpus-2013/
You can see,Maya is very improved in Amd cards, since 2008 until a few months ago, i was using an Ati radeon hd 4670 with arctic l7 as a cooler. This card surprised me, could hold more than 1 million polys with reasonably good 1024x1024 textures in Maya 2013 with 30-50fps. In Autodesk Max with the nitrous engine,almost same results,very happy with it. But well,i needed cuda and directx 11,so few months ago i bought an gtx 580(pretty old powerfulish cuda gpu).
I think that the newer amd radeon have enough power to surpase the nvidia equivalents due to fp64(nvidia kepler is sooooo limited in compute...)
For the disks,i suggest than some 3d models or some programs that not consume a lot of writes of the disks go to the hdd,for save space in the ssd.
Then,the other program, Zbrush,this only uses 1% of the gpu,the lightbox only uses the graphics card,the program itself is rendered by software,the cpu is who makes the fps in your 3d models,the ram who breaks the limit of the Total polygons of the model and the disk(ssd or hdd) who makes the model not "freeze" or slowdowns(because load of polygons and textures) in the viewport of Zbrush.
Well,this thread it´s a little old,but i think this info could be useful.
For my experience&benchmarks in Zbrush with my rig( I7 3770k&3.5 stock, 16 gb ram g.skill 1333 cl9, Samsung evo 120gb, nvidia gtx 580 undervolted&0.988v stock clocks):
Máximum polygons(limited by my 16gb of ram): 22.5milions
Máximum res o textures: 8kx8k
Bottleneck of the ssd,when i´m working with arround -20milions with 4kx4k textures(use of the ssd in this moment 95-100%) and stuttering like watch dogs game i have. Note that the ssd is in SATA 2 because of the motherboard, an old gigabyte h61m which i need to change.
Use of the gtx 580:1% with lightbox opened,if not opened 0 %.
Well sorry for my bad english,i´m from Spain and this is my first post in tpu.
PD: (Spaniard language): Darksim10 al parecer eres tambien español por lo que veo,luismiguel en amazon .es no?