Hi mate. You can definately make significant gains naturally. Check out
www.lamuscle.com. A mate of mine did a natty show at the weekend and the pictures are posted on that site. There are some pretty significant bods there.
Why not post up your training programme, diet and supplementation and we can have a look and maybe gives some tips. Post your stats (age, height, weight etc and what your goals are) As long as you've got the commitment, you're halfway there.
My personal opinion is there does come a point where the gains slow down to a point that only gear can break through. Or, you decide to take your bodybuilding to another level and think about competing, where of course, steroids will help enormously. As you say, it's a personal choice. But before making that choice, do the other stuff I suggested (i.e.post your training,diet etc).
Nice to have you on board