Pianoteq has come on in leaps and bounds since it first came out, however if I were really into piano I would still go with
Pianissimo as I find it to be more flexible. (You can download trial versions of both)
When I used to a single core Pentium and 2GB Ram in my Abacus it ran Pianoteq with commensurate ease (You wouldn’t have known you had anything extra loaded) and as the latest version is even more CPU efficient I wouldn’t worry about running out of steam.
NOTE: Sound modelling is more tied to CPU than memory, whereas sampling not surprisingly puts more pressure on memory rather than CPU.
Using disk streaming (Which has been the standard for donkey’s years with sample VSTis) you will find you will not need masses of Ram, but like all things the more you have the merrier. (Just don’t go overboard)
Bill