I have gone in stages. When I was younger (1980's) we'd pack in with less than adequate equipment and freeze our rear ends off. Lack of good technology and lack of money ensured that we had the heaviest of gear that still didn't keep you warm or safe in heavy snow, winds, or cold. So went to truck camping and was still very doable and we still killed a lot of elk and deer. However, I found that I was covering 15+ miles a day, leaving camp well before first light, and returning well after dark. That's all fine and dandy when you're young, but now that I'm almost 50.....those 5 mile hikes in and out are the majority of the day's hunt. Multiply that times several days and.........well, it's suddenly better to carry your camp in, set up, and hunt from there. However there are also those hunts where I want to cover a specific range, so need to have my camp on my back and not set up somewhere I won't be at the end of the day.
For me, "far" never really is quantified until the packout. Packing in is easy, and there really is no limit to that.......go until one is down. But there is definitely a "too far" when you're packing out. That cow I shot 6 miles from the trailhead........that was "TOO FAR" for a cow. The bull I shot last year was almost 5 miles and I would have gladly hauled him twice that far. So it's all relative for me.