RE: How do I get something medium rare?
The surest way is with a meat thermometer: internal temps: Rare=135-140 degrees, Medium rare=141-146 degrees, Medium=147-150 degrees. They now make thermometer/forks that you can stab into the meat and check the internal temp periodically as it cooks.
I don't know much about convection (you did mean convection, not "convention" didn't you?) ovens, but it's hard for me to imagine cooking STEAK (as opposed to a roast) in any oven. It's a lot easier to cook relatively thin cuts like steaks and burgers on a hot surface like a grill or frying pan or with direct heat like a broiler.
You should not need to fear bacteria in a solid cut like a steak. The harmful bacteria in question are from the intestinal tract of the animal and can contaminate the SURFACE of cuts of meat but they do not get inside it. The problem with burgers is that the meat is ground which distributes anything on the surface of the solid cuts all the way through the ground meat. But with a steak, just rinse it off and pat it dry with towels (paper or otherwise) before cooking. That plus the fact that the heat is applied directly to the surface where any critters are and almost certainly kills them will keep you safe. But burgers are another matter and if you like them rare (or less than well done) you have to take your chances or grind your own (or possibly have a good butcher grind it for you--we discussed this in another thread).