First off, a periodic sampling will only give you very vague information that is of little value unless it displays very high readings, which yours doesn't. As for what CPU load is acceptable, that's not easy to answer because you need to examine both instantaneous loads as well as longer term figures.
While this will vary between makes and models of CPU in general you don't want to sustain loads greater than 50% for extended periods. Quite simply, CPUs are not designed to handle that well and the resultant heat within the chip itself will be problematic. There is a limit to just how efficiently that heat can be transferred to whatever heatsinking you have, so simply adding more cooling isn't necessarily going to solve the problem for a highly stressed chip. For this reason it's important to also monitor the CPU temperature, as that is far more significant than the load itself. Consult the manufacturer's specs to determine what is good, bad or ugly.
I also suggest you shorten your sampling time as much as possible, at least while you are establishing a baseline, as that will give you better accuracy. If you don't see and significant load over 50% I really don't think you have a problem. Remember that short spikes, even up to 100%, are not a problem provided the average is low enough to allow the heat to escape.