I realize the bulb wattage is limited by the stators output.
I've been researching the base type and believe it is a p15d25-1 (my bike is a 250D2).
15mm dia. base with a 25mm flange and seems to look similar to the H6M
from PIAA. Stock is 30/30 watt and the PIAA is 35/35 but has a (equivalent to)60/60 output.
I have a UFO rear fender on the way so the tail light is history for now which would help.
I see the H6M advertised for $9.00 on one site even though it has a msrp of $30.

I searched this topic but didn't find much