What rings your bell in this situation? The fact that it spikes to 100 or that it stays on 80 most of the time? When CPU usage is low (for example 30%) while rendering is a sign that there is a of bottleneck somewhere. Maxing out the CPU while rendering is good, it means that some work is done and CPU is not sitting on its ass. 80 as average is good enough I think, because some time goes into reading stuff from RAM, writing other stuff somewhere, doing some single-threaded routines and CPU is not 100% fed all the time.
I was just surprised it was hitting 100% . Also i have been reading about rendering with your GPU. Is this a good way to go or is it not worth it or about the same eather way?
Improving CPU rendering at the small scale is initially cheaper - switching from a quad-core to a hex- or oct-core processor and adding some additional RAM is pretty cheap compared to purchasing a high-end video card such as a Titan X or 1080. But it gets more expensive at larger scales as you need workstation motherboards to support additional processor chips and associated RAM. Not only do processor costs increase, but unless the computer is spending a lot of time rendering those extra cores are sitting around doing no work for you. At that point GPU rendering gets more cost-effective, even if it does have some limitations.
In short, if you’re using this to make money invest in a good video card and switch to GPU rendering. Either way don’t get tunnel vision regarding rendering requirements; if you are considering producing anything longer than a few minutes on an irregular basis, its time to start evaluating online render farms vs. upgrade cost/render time/render quality. You can build a much cheaper system that can do fast modeling and some simple test renders, then apply the savings to a very high quality finished product.