It's better not to use more than 35w ballast due to its closed design. The extra heat captured inside the shroud might damage the shroud after some time. But i've heard some people still using 55w ballast with the stock shroud.
i was swapping my newly rewrapped steering 2 days ago... and to my horror, the Air Bag light at the dash suddenly came up blinking... checked every single connection and i am very sure i didnt break anything...