I don't know too much about electrical issues or what's best. But I have heard that 55w can be hard of your truck's headlight housing. They can get too hot that the plastic could warp, and no one really wants that.
I was actually looking into what would be the brightest bulbs for my high beams. A friend recommended 55w, but not to run them too long for this reason. I would only really use them for a few seconds.
Sorry guys! my english is bad. What I mean is, the European models are fitted with different headlamps. We do not drive with the running lights, but we use the low beams at daytime. The lamps are therefore designed to withstand the heat from a 55W halogen bulb continuisly. What I would suggest for you guys who want to run 55W HID`S is to check if the export headlamps maybye would take the extra heat the 55HID`S produce, compared to the 35W HID`S.
I just checked my headlamp, and it`s clearly marked "EXPORT". So I believe there is a difference. But, here in Norway there is limited info on these trucks. So I`m sorry that I cant provide accurate information on what the difference really is.