Assuming an Older Quad core CPU, ticking off one core should Theoretically see a 25% drop in Speed.
The Impact with Modern Hex and Oct Core CPUs should be less. Also, Now that we use GPU for Rendering, the Role of CPU is Further Diluted.
Combining above factors, I’d take an educated guess that Your Exports may take around 10 to 15% Longer. But on the other hand you Gain Massive responsiveness for Other Light Tasks. If you want me to do a proper speed test between these Optimizations, do Comment on That particular video and I will make a quick Benchmark on it.