I own a few 7mm-08s and believe that it is the ultimate whitetail cartridge up to about 300 yards. Can it take deer down at longer ranges? Well, I personally haven't shot at a deer above 200 yards, but I know of some that have with no problems, BUT that was because they were very good shots which, after all, is the most important consideration.
In addition, although shot placement is very important, from a purely numbers perspective, consider the following:
Bullet design can increase your downrange velocity, energy, and trajectory. For example, if you use a 140 grain blunt-nose, flat based bullet from a .280 Remington, and use a 140 grain sharply-pointed plastic tip boat-tail bullet from a 7mm-08, then I'll bet you that, assuming powder charge is the same, the 7mm-08 will equal, if not beat, the .280 past 200 yards or so.
Of course if the same bullet weight and style is used, then the cartridge with more powder will push it flatter, faster, and harder, but you can take advantage of new bullet designs to get that extra "performance." Again, shot placement is the most important, but from a pure numbers perspective, you can essentially "up your gun" by using these new more aerodynamic bullets at longer ranges.
Keep in mind that most people shoot at ranges of an average of 100 yards or so, at least out east. Perhaps in the west it can average in the 200 yard range I guess, but still, few people take these 400 yard shots.
Zachary