To me, bullet construction is a lot like gas octane. You only buy the 93 octane gas if the compression ratio of your engine forces you to. Otherwise you are wasting your money on the more expensive gas. It gains nothing to put 93 octane gas in a 8:1 compression engine.
Same for bullets. If you are shooting a heavy for caliber bullet in a cartridge that is mid-sized for caliber, then the velocity is going to be relatively low and a cup & core bullet will do the job perfectly. Examples of this would be a 308 with 165 grain bullets. It can't push them fast enough to justify a premium bullet. Moreso for such cartridges as the 7mm-08 or 260 Rem with bullets of 140-160 grains. If you are using a 30-06 with 180 grainers, same situation.
Where I start to see a need for controlled expansion bullets is when velocities begin passing 3,000fps. OF course, the speed your bullet is going at impact is what counts, so you can get away with a more fragile bullet for long range hunting than up close shots. The bullet will slow down enough crossing a big field to survive impact and not fragment in the deer.
As far as the solid copper alloy bullets, I can't see them justified for deer except for the ridiculously high velocity cartridges when hunting in places where your shot could be up close. For example, I use the Barnes TTSX 100 grain in my 257 Weatherby in a 3,590fps load. Beyond 200 yards any bullet should hold together loaded at that muzzle velocity, but up close I personally don't trust a standard cup & core bullet to hold together at that speed.
I would absolutely trust a Nosler Partition at that velocity however. They are the best of both worlds from my observation. You get an explosive nose that opens up - transfers lots of energy - then the base retains 60% weight and punches all the way through to give you 2 holes for blood loss. As soon as I shoot up the TTSX's I have, I may switch back to my old faithful Partions.
