The D4 geared, does offer you the ability to make very fine micro adjustment, and unlike the BH55, allows you to free up one hand (I also have the 55). Using a tech camera, this made a big difference for me.
The D4 geared, comes with both a lever lock and screw lock top. The lever lock is great, but won't auto adjust, so if you moved between platforms, RRS L bracket, Kirk L bracket and Arca, it can become a bit of a hassle. The screw lock prevents, this but also sticks out a bit more. In the older day's it was possible to change out the Arca Lever Lock with the newer RRS version, (which does auto adjust), but Arca has made this a bit more difficult as they use a very strong thread locker.
Weight, I would say is very close between the two, BH-55 and D4 geared. The D4 is more delicate, I carry it off my tripod in the field, never worried about the BH-55 and mine shows some use.
You can also reach out to Rod Klukas, the US Arca rep, based in AZ. I don't have his contact, but he can be found quick on google.
Paul C