Do Core i7 heatsinks have the same geometry as my core 2 duo CPU's heatsink?
From the look of the stock heatsinks it would seem that they do, however I would like to be sure before moving my Zalman.
You should check if you have the correct mounts for your Zalman. The instruction manual for my Noctua says the mounting holes for LGA775 are 3mm closer to the center of the socket than LGA1156 which is itself 5mm closer to the center of the socket than LGA1366. Unless your Zalman has the correct mounting holes it will not fit.
This is how newer heatsinks handle the size differences:
If you compare a:
Core 2 heatsink:
with a Core i series heatsink:
They are pretty much the exact same; the Core i7 heatsink seems to have longer fins and a better looking fan thus providing better cooling than the Core 2 heatsink.
However if you're looking to overclock, I would definitely prefer aftermarket heatsinks than the stock.