Once again, being busy leaves me catching up in the conversation.
James, the reason there aren't any heavier true spitzers in .277 is because they're not needed. If it can't be done with a 150gr spitzer like the Nosler Partition or other premium bullet, it's not getting done with a 160-175gr, either. If you look at SD and BC, the 150gr .277, 160gr .284, and 180gr .308 all carry roughly the same values. In fact, it's the overall weakness of the .284cal that requires it have the heavier bullet weights to make up for it's shortcomings. In life, we call that "compensating for something."
@Hunter - I'm surprised at the 3300fps 160gr loads. Even pushing all the limits of real pressure standards, I find 3300fps with those more like a 7mmSTW (akin to the 7mm-300Wby), and probably well into the 70-75kpsi range. How are the primer pockets holding up on those brass?
And for the record, I own a 300Wby, and yet I still prefer to hunt with the 270Wby. If you owned one, you'd understand. One day, even James will see the light and come back from the dark side of the force...