on my A7ss i fitted a cibie Z beam headlight unit, way better than anything else i have tried and it has an h4 fitting, converted to 12v and LED lights all round and i now have decent lights that i can use on very rural roads as that is where i live, no street lights out here. total load is now less than 30 watts so the dynamo does not struggle to charge even with the lights on, got the srm belt drive kit fitted as well, works fine and i can see where i am going. fitting higher wattage bulbs does not work very well as the dynamo only gives out 60 watts if all is working correctly, so a 45 watt bulb plus stop tail spedo and pilot light is to much for the dynamo , i have found that using a slightly less wattage bulb that can run at full power gives a better light than a higher wattage one that does not have the power to drive it properly, if fitting a headlight with an H4 fitting there is available an Osram nightbreaker bulb at 35/35 watts which i used in my bantam and that was very good and the bantam only has a 50 watt alternator and has to run the ignition as well, i think going to 12v these days is a much better idea and there are some decent bulbs you can use which are not available in 6v.
one other way to do things is to fit an Alton in place of the dynamo and then no problems as you can then run a standard 65/55 h4 bulb at 12v and easily charge the battery.
done this on another A7 and for night use it is very good but even that i have now converted to LED as it is so much better, but you need to get a decent LED not some of the nasty cheapo ones that are now appearing.