A benchmark would depend on too many factors. The speed of the hard drive, cache size, SSD type (SLC, MLC), and quality vary too much to say an SSD is x better than a HDD in all cases. I've used SSDs in newer Dell laptops that are barely faster than the 7200RPM drive I have in my older Dell laptop. I've used some real nice ones that are ridiculously fast.
Regardless of speed, it's worth noting a few things outside of speed benchmark. They are silent. They use less power, and generate less heat (granted these concerns are a bigger deal in a laptop than desktop) but some of these extra benefits are worth it even at the same speed if price isn't an issue.