Claude,
Ok here goes frame geometry has nothing to do with strength. Strength of a frame is in the tubing material selected and its assembly. Example a tig welded high tensile steel frame is not going to be as strong as lets say a tig welded Tru-Temper OX III frame. Diferent frame tubing gives you different ride qualities. Example Cro-Mo steel comes in many different alloys from many manufacturers. Each frame from various makers will feel different depending on tube selection, angles, and assembly process. The "bend" in a fork...well from here on we will call it rake. The rake on a fork affects steering. It also affects how the front wheel distributes shock. The straight rake disapates it right to the headtube and bars. The more sloped rake will use more of the wheel to disapate shock. Seat tube angle will affect your body's position on the rear end, and also it has an affect on weight distribution on the rear end. The stem length, the shorter the stem the faster the steering, however it may have a profound impact on the way your body is positioned on the bike. Ideally on an adult diamond frame you want you elbows to be plumb with your knee at the bottom of the pedal stroke, with a slight bend in your knee. You also want to have a slight bend in your elbows and back upon reaching this position. For more detail see my website. The link is at the bottom of this bar. Go to frames there is alot of links to help you.