Factory halogen bulbs operate at 55 watts. Using a higher wattage bulb will produce more light but the output will still be dim compared to a true HID system. If you choose to use higher wattage bulbs, you increase the current draw on your entire electrical system and run the risk of melting your factory wiring or harming the rest of your electrical system.
A true HID system runs at 35 watts while traditional halogen bulbs are 55 watts. Even though XENON HID lamps draw less current, they produce 3 times the light output as the higher wattage halogen bulbs.