It varies with velocity and bullet shape. Higher velocity and/or pointier bullets shoot "flatter" compared to slower and/or less aerodynamic bullets/loads. The term for man aeordynamic bullet is ballistic coeficient. The higher the number, the more streamlined it is. Neither the 110 gr carbine bullet nor the 220 gr round nose are very streamlined compared to many other options.
The thing about "nosedive" is, the more aerodynamic a bullet is, the farther it travels before it begins to trend downward. The pointier it is, the less air drag and less drop for a given range. The time factor isn't as relative to the topic as how far the bullet goes in that time.
If a 30-06 kicks your butt, a 308 wont be much different with similar bullet weights. There just isnt a lot of difference in power levels until you get above 180 gr bullets. A lighter rifle will also have more felt recoil, all else being equal. The 308 can do 200 gr loads alright, the '06 does 220's, though there isnt a lot of need for the heaviest for most uses. Premium grade medium/heavies penetrate about as well as standard grade heavier bullets. Also, be realistic in what you are going to do with it. If you arent shooting moose and grizzlies in thick brush, the abilty to use the heaviest loads isnt that much of an issue.