Each Txx series has the Txxp model (notice the p suffix) - it is a model maximized for performance. Usually, those models contain an extra video card from professional series FireGL from ATI/AMD and Quadro from nVidia.
I found this site who can tell you in details what each series is made of (but you can see this on Lenovo site, with more searches and clicks): http://www.thinkwiki.org/wiki/Category:Models
