Is that % an ASIO Performance or OS measurement?
If it is the OS measurement, it might not be including the peaks. Audio recording relies completely on the peak CPU use for glitch-free performance, though forcing execution to spread across CPUs has helped alleviate pressure on one.
I have noticed that Cubase tends to favour CPU 0 more than others, but it may be the one the GUI thread is on. Of course, it only takes one CPU to overload to get glitches.