If you have a FEL on your tractor, most any bulb is going to be almost worthless. At least that is what I have found. I have a 7800 and mounted a couple 55 watt forward pointing lights on a piece of angle steel and attached that to the ROPS. It does make a big difference. I have one 55 watt flood light pointing to the rear. The front and rear are on separate switches, and I do not use the factory headlights. I seldom run the front and rear at the same time. If so, only for a very short time. I have not upgraded the alternator, but we'll see if it becomes necessary. Hope not.
If you don't have a FEL, then I don't know about brighter bulbs. However, this is my first tractor, so I have nothing to compare it to. With the FEL on the ground, the factory headlights seem acceptable. Just my take. Good luck.