China Cat, just noticed your post and wanted to say the folks above are correct. There's no such thing as "piano tab". I assume what you're calling piano tab is chords over lyrics....I'm not sure what to call that but it's not tab like guitar notation is tab.
As for sheet music, most of the time, it's an arrangement or a kind of orchestrated version of the song so if you play it as written, you're actually playing other parts, not necessarily just the piano part. On rare occasions, the sheet music will in fact be the actual transcribed piano part. generally depends on the book. ie The ELP song book I have is actual piano parts--not orchestrated arrangements of the overall song. A Pink Floyd book I have is just an overall orchestrated arrangement. The GD Anthology is like the PF book. It does not have actual piano parts (with an exception or two, like the piano lick for Unbroken Chain).
Sheet music can be helpful though to get an overall sense of the tune and help with possible chord voicings. If you really want to learn the "piano part", usually you just have to listen to the tune and figure it out for yourself.
Hope that might help. MT