The stock wattage on an H4 Hologen, which is what is in our sled from the factory, is 55watts low beam, 65 watts high beam. The wattage of a sylvania silverstar is exactly the same, the difference is how much whiter the bulb is, and the color temperature, it creates more lumens which create better visibility, more crisp, not as dull. If you put in higher wattage bulbs you risk melting you wiring harness and possibly the light housing. Just be careful. Thats why I went with the silverstars. PIAA also makes a high performance bulb like the silverstars but I havent seen those in action.
Peace!