FWIW, I've done some pretty heavy archvis-type scenes with Redshift. Several million triangles (usually straight out of CAD, so, yuck), a few hundred ray-traced area lights, an HDRI dome, about 50 MB of textures (so not very much there), TONS of procedural noise textures, bump maps on most surfaces, up to a couple million instanced small objects with emissive materials, with depth of field and motion blur, for HD and print resolution, etc. RS has chomped through all of it in very reasonable times and without ever challenging the memory limit on the Titan. Can't share any scenes or images though. :-(
One note on the "expense" of a Titan -- I have a pair of them in an early-2008 4-core Mac Pro Bootcamped into Windows 7. For a proper lighting/lookdev station running VRay, Arnold or Mental Ray, I would have to spend well north of $8000 on CPU & RAM alone and still wouldn't have more than a fraction of the performance. The Mac Pro could be had for under $2K (although it was "free" to me as I bought it new and it's been fully depreciated) and the pair of Titans for about the same. By upgrading only GPU instead of CPU & chassis, companies will be able to double the lifetime of their CPU purchases, perhaps more. And the upgrade cycle costs will be significantly lower per-seat. The Titans certainly paid for themselves on the first project they rendered. I'd feel differently about the changeover costs If I already had a sizable render farm, since most of the blades and 1Us that people have invested in can't even carry 1 GPU card. But if you are building out a new place or growing the farm, you can pick up 1U servers built for Tesla-style GPUC clusters that have power and slots for 3 beefy cards. Since you won't care too much about CPU specs, you can buy ones that are being retired on the secondary market pretty reasonably. Once it can handle ICE attributes, I'll have no reason to look back, EVER... Also, someone was wondering about SLI -- RS doesn't use it; it handles multiple CUDA cards just fine without it, even if they're very different cards.
