I have the Hella H4 conversion headlights on my 1955 classic since 2002. Originally I used the Hella +50 bulbs that came with the H4 conversion headlights,and they were much brighter than the stock headlights. These Hella bulbs had the same amperage draw as the stock headlights, so there is no issue with regards to upgrade with a new harness and relays. Years later, when one of the Hella +50 went out on the low beam, I was looking for an immediate replacement, as the bulbs had to ordered and shipped (3 to 5 day wait). I did some research and found out that the Silvania Silverstar bulbs were even brighter that the Hella +50 bulbs, and still had the same amperage draw as the stock headlights. I was able to immediately purchase the bulbs at Napa, Autozone, O'reilly's, Pep boys, etc. After installing the Silverstar bulbs, my fog lights and driving lights looked orange in color, compared to the headlights. So I changed out to Silverstar bulbs in these lights as well. A year ago one of the Silverstar bulbs went out on low beam, so I replaced it with the Silverstar Ultra, which is even brighter than the standard Silverstar, and still had the same amperage draw as the stock headlights.
The higher amperage bulbs are fantastic, but required heavier wiring and relays, due to higher amperage draw, to prevent burning up the light switch and the existing harness. These bulbs can be hard to find, if you don't carry a spare set with you.
For ease of replacement, as well as availability, when on or off the road, I have been very happy with the Silverstar products. I still have the original light switch in my 1955 Classic, and have no problems with any of the wiring harness.