First of all... dat hardware list is SO strong x-).
While I don't personally do anything in terms of 3D rendering, I would seem to think that if your software supports GPU acceleration based on the architecture you use that you would need to do several different rounds of performance tuning on the GPU(s) as well as the CPU(s) to determining where the best happy medium is located: no sense in overclocking just for the sake of overclocking if the performance benefits you gain don't match the effort put into the overclock as well as the increased operating costs (minimal as they may be). Using benchmarks that pertain directly to your application certainly helps, and using those benchmark scores you can see patterns starting to develop as you push your silicon further and further.
Eventually you can and will get to a point where the performance gains you net aren't worth the effort it took to get you there or the uncertainty of system instability occurring in the middle of a heavy rendering session. If it were me doing the tweaking for a machine like that I would honestly only tweak it minimally, that way I can keep the system running strong but quiet as well. Performance for the sake of performance starts to sound not entirely unlike a top fuel dragster after a while, and that's just not enjoyable to work around even if you DO have headphones on and are listening to music (which will probably run like balls once the CPU cores get fully loaded with render tasks).
To relate to what I have observed in overclocking for my system (in my case for gaming and for hardware reviews), I have definitely noticed that as I tune using PCMark, 3DMark, Cinebench, WinZip and others, there will come a point that, while I might have gotten more out of the hardware, the scores start to predictably, though exponentially, fall off and eventually hit a sort of asymptotic point where you just aren't going to get anything more out of it without moving to extreme measures, and that's just not worth it. For a machine of the nature you speak of, or even a simpler machine like mine, it should be functional in many ways, not just for doing it's intended purpose. Personally, I feel like if you can get anywhere around a 10% performance increase out of any of your hardware then you're solid for a workstation: focus on keeping it cool and quiet from there.