It is all a compromise.
Gravity is a constant, so "Flat Shooting" is all about velocity. In reality, it is not that important at normal hunting ranges. Zero your rifle at 200, and hold high a bit at 300, or you can adjust your scope. How much you hold off with one cartridge vs another is really irrelevant, provided you know the number for the rifle you are shooting (~7.5" for the .30-06, ~6" for the 270). Where "Flat Shooting" is a benefit is when you get the range call wrong, but in reality, at reasonable hunting ranges, it is not enough to matter.
If you think Bambi is at 300 yards, and he is actually at 325, a 150gr .30-06 will be ~3 inches low. A "flat shooting" 130gr .270, in the same situation will be ~2.5 inches low.
At longer ranges, you call the range 500 yards and it is really 525, the .270 will be 5.6" low, the .30-06 will be 7.7" low. Assuming a perfect hold and shot, both would probably still hit, but neither would be a good hit, most likely. Most people have no business shooting that far anyway.
Keep in mind too, that drag is based on the square of the velocity, so higher velocity bullets shed speed quicker the faster you drive them. For example, even a bullet with a pretty good BC, for example the Hornady 6.5mm 140gr Extremely Low Drag Match (0.610 G1 BC), if you somehow were able to launch it at 4000 fps, it would lose ~175fps in the first hundred yards. At a more realistic but still fast 3000fps it loses ~160fps in the first 100 yards, and a pretty slow 2000fps it drops ~128fps.
If the bullet sucks ballisticly, for example the .17cal 20gr Hornady VMAX (0.185 G1 BC), from a .17 Remington at 4000fps loses 638 FPS in the first 100 yards.
You also haven't mentioned sectional density, witch for a given caliber increases with bullet weight.
In other words, for most North American hunting, as long as the cartridge is of adequate power, and you use an appropriate bullet, any of them will work fine, and if you do your part, Bambi won't know that he was hit with a 90 gr .243, 140gr 6.5 Creedmoor, 130 gr .270, 180 gr .30-06, or a 200gr 8mm Mauser, or anything in between.
So in other words, here are most of the things you need to balance when deciding on a cartridge.
Sectional density
Velocity
Energy
Ballistic Coefficient
Barrel life
Recoil
Cartridge OAL (short/long action)
Ammo/component availability
If I was shopping for a general purpose, sporter weight hunting rifle, I would probably look for a 6.5 Creedmoor. The .264" 140gr is a sweet spot for all of the above except ammo availability (you probably aren't going to find it on the shelf at WalMart), but reloading components are readily available. With the 140 gr hunting bullets (Sierra GameKing, Hornady Interlock, etc) it is fine for anything in the lower 48 short of big bears, and I wouldn't hunt those anyway. There are also light (<100gr) varmint bullets available.