Hello, hard for me to tell you whether or not the Mac Pro 5.1 will go faster with Mojave. I just spent the day with Mojave and actually it is more responsive and more stable than High Sierra. But for now I re-installed some applications as and when my needs.
By cons I feel an improvement with the GPU Sapphire RX 580, it is displayed at 5 ghz (2.5 ghz before with High Sierra) and seems to accelerate more the finder.
I already find this first version of Mojave more successful than High Sierra (all versions) which is very good.
Note however that my wifi card is no longer recognized, however, from memory it was not in the list of unrecognized cards.