The stock w124 NAMs use 45W/65W bulbs. 45W is for low beam. The stock w124 Euro lights use 55W/65W bulbs. There is a 10W difference between the two. Combine that with the superior lens of the Euro beam pattern, and you'll see why a lot of folks convert to these Euro assemblies.
I too tried the XtraVision bulbs before with sealed beams on my w123 before I switched to Euros, and I kept adjusting the beam because I could find a suitable setting. Now with the Euros I just adjust it properly and be done with it.
Additionally, and this is from my observation so far, I notice that the W124 and W201 (I don't have a W126 to observe) NAM lights, the bulb plug has insulation material. What I've seen so far is this insulation material degrades over time and causes the plastic to melt or burn, leaving you with no low beams but with high beams (or vice versa, but having low beams only is better than high beams only). My sister's 190E had this problem and we had our mechanic solder in a new plug/socket to get her lights working again.
http://www.peachparts.com/shopforum/diesel-discussion/332624-melted-headlight-plug-w124.html