I can't tell you how current incarnation runs on the PC - I've switched to mac 6 years ago. Back then, I though it was under-performing compared to Sonar, Cubase and the rest of them.
What I can tell you is that compared to Logic, it performs awfully poorly. I was going to mix a project in PT a few days ago - I imported 26 audio tracks, some stereo, some mono. No plug-ins and the buffer set at 256, I kept getting drop outs just playing back the project.
Logic lets me run projects 3 or 4 times that size with virtual synths and samplers, automation, live input monitoring and dozens of plug-ins, and I rarely ever raise the buffer anywhere higher than 64, if at all. In fact, I have yet to push Logic to its limits...
Same Mac, same audio interface. From memory, Studio One performed pretty much like Logic. Cubase was not far behind.
Maybe Pro Tools is allergic to me.