Monolithic copper bullets perform better at high speeds, but the speed drops off faster, the quicker they are pushed. At regular "big game rifle" speeds, the cup and core perform more reliably, over a wider velocity range. If I was shooting a really hot, high speed cartridge, then I would probably lean toward a solid copper bullet.
Less SD, and less momentum than a heavier cup and core. The solid copper crowd tells me that because they usually lose less mass, that it's equal. I may consider that to be a valid point with a higher speed cartridge at very close range, but I am unwilling to give up performance at longer range, where people are using monoliths under the assumption that they are gaining something.
Cast bullets are the original mono metal, and widely recognized as superior at lower speeds!