I always have content stored on a separate drive. One reason is that if the drive gets too small it easy to replace it with a larger one.
With content space requirements getting more intense (I think my total RL content is over 1GB), it certainly makes sense to use a separate, large drive.
There are no benchmarks as to the difference in load times, but since project files can now also be over one GB, an SSD may help. Others may have a more definite answer.