Actually, that would not be an upgrade because the Titan Z is of the older Kepler generation, versus the newer Maxwell generation of your current 980 Ti. What's more, the Titan Z actually consists of two GPUs that have been "permanently" linked via a non-defeatable SLI, which can (and does) cause problems in Premiere Pro.
In other words, you would be trading away 2816 fairly efficient CUDA cores for 5760 less-efficient CUDA cores which may only end up being half-used simply because Premiere Pro has been known to choke on SLI GPU configurations. In the worst-case scenarios, the Titan Z with its non-defeatable SLI will lock Premiere Pro to the MPE software-only mode, with no GPU acceleration available.
A better upgrade would have been a Titan Xp, not a Titan Z. However, your CPU, even when overclocked to 5.0 GHz, is not powerful enough to fully utilize that Titan Xp. And even your current GTX 980 Ti is quite overkill for your system's CPU.
If you were working with 4k, and your quad-core CPU stays below 50%, then it is very likely that you have something else outside of the GPU that's bottlenecking your CPU. You may have an excessive number of Windows processes that prevent Premiere and its encoders from accessing the CPU.
If you want to know your system's GPU utilization during the exporting process, download and install GPU-Z. If the GPU utilization is also low, then (like I said) it is likely that something else is bottlenecking your system.
Thanks RJL190365. That is what I wanted to know. I will try GPU-Z and see what is going on.
The weakest part in you system in your system is the 4-core CPU as Randall asked how many processes do you have running?
Look here. This is unusually low count of only 41 and did not come from a normal setup but you probably should see about 70-80 on a well tuned system,but it was the only thing I could find that had a Win 7 OS .
As an example do you have indexing turned off on your SSD's