This is a very good question and it is smart that you ask...

First of all...if you take normal long strides, like you see a ref at a football game do, you will be pretty close in accuracy, so your initial 30 yard estimate might be correct. Also, when you are in a different environement, the way the yardage looks may be off, hence, why you think it might be closer to 50 yards. I bet your first guess is correct.

Next, when you are hunting, everything changes. Your setup, nerves, everything is different. You might be better limiting yourself to 30 yard shot on in. That is just one persons opinion. You will find that hitting a deer at 30 yards is a heck of a lot tougher than a target at 50.

Still, it all comes down to you. Use this rule. At what yardage do you think their is a fair chance that you might wound, not kill, the deer, and that you may have a too difficult tracking job. Whatever this is, go back from that spot. For me perosnally, it is around 35 - 40 yards.

Whatever you come up with, kudo's to you for asking that questions. Successful, and rewarding, hunting is not jsut about what you harvest, but about HOW you hunt.

Good luck bud!