Having done some research and a fair bit of experience diving with both types of sharks ,I'll give you this-Grey Reefs probably come into contact with humans more often because they more often frequent the waters we dive in,there are more of them,they can be aggressive if you enter their territorial space,but unless you agitate them or you are bleeding or chuming the water somehow (ie,spearfishing),or swimming on the surface,you are going to be fairly safe-though if you accidently enter their space be prepared to possibly push them off (with a knife,camera,gauge,fist,anything) if they come straight for you. They will usually arch their back and lower the pectoral fins and swim in smaller circles first before they do that though. The Silvertips, on the other hand,are a much larger, deeper water shark-and in my experience,act more like Oceanic Whitetips-very curious,will bump you -will keep circling, looking at you more as potential dinner- for example,I've had a 12 footer swim right up to my wife and I and we had to split apart so he(?) could swim between us-kept circling at arms length-totally unafraid. The only other shark I've dove with that gives me the "lower food chain feeling" as much as a Silvertip, is a Tiger shark-who will also make you feel lower on the food chain. I've dove with all the other major aggressive sharks (except the Great White-who I assume would provoke the same feeling in most of us-and I have no desire to swim with a great white in the open ocean-though it has occassionally been done),and when I see a Silvertip, my caution level goes way up.Not that you should panic,but do realize that this is one of the top apex predators in the ocean and stay very alert. Again be ready to push them off if they come straight at you-they will likely swim away,though it could take several bumps and pushes to let them know that you aren't an easy meal. Though I've spearfished in waters with Tigers,Great Hammerheads,Bulls and Grey Reefs-I would not even want to think about being in the water with a speared fish and get one of these guys frenzied....food for thought........Peace.......Saildiver.