There's a thread somewhere discussing this and as I recall, he tested both standard 35w and 55w HIDs. He concluded that 55w is OK for the wiring and is significantly better for light output. That doesn't actually confirm what he fits in the kits he sells, but it seems like you can make safely a choice either way.
I'll try to recover the thread.
EDIT:
https://www.the75andztclub.co.uk/for...d.php?t=277886
TC