I bought PT 8 m-powered over Christmas to learn the software. I was stunned at how few soft synths I could use in it compared with Cubase 5. It was so disappointing that I sold it. I think that the resource requirements of Omnisphere bump up against PT's resource limitations in the areas of RTAS CPU and RAM inefficiency and the RAM limits due to PT being a 32-bit application.
After running 64-bit synths in a 64-bit host, I don't want to go back.