A bulb blew in my car, so I did what any rational person with a little time and the internet would do … and went down several rabbit holes to find what would be the absolute best replacement. The alternative would be to buy a perfectly acceptable bulb in about 5 mins, but where would the fun in that be.
This search brought up two main options, the Philips RacingVision GT200 and OSRAM NIGHT BREAKER 200. Both are essentially identical and at the time of writing (and as far as I could see) the brightest halogen options available producing 200% brightness (1,500 lumens) compared to the minimum legal threshold.
On a few Amazon entries, the GT200 were listed as 3,500 lumens but this looks like false advertising as on all other entries the bulbs were listed as 1,500 lumens which also matched the 200% brightness claim.
The only measurable difference between the two is that the Night Breakers are 50K colder at 3,550K (compared to the GT200s at 3,500K). Reviews then pointed towards the GT200s putting more light on the road ahead due to the precision welding and optics of the assembly. This would have the advantage of making the bulbs effectively brighter for the intended use.
After a few videos (and assuming that the tests were fairly conducted) this claim by Philips seemed to be false with the Night Breakers actually delivering more light to the main-beam cone, 3,280 lux at 3 meters for the Night Breakers vs 2,770 lux at 3 meters for the GT200s. The video of the test is below (2:53).
The above video also showed journies with both bulbs for a similar journey and whilst highly subjective, the Night Breakers seemed to deliver a better result.
One line summary
So whilst essentially identical, if you care about minutia detail, the Night Breakers come out fractionally ahead, being 50K cooler and developing greater forward luminosity under real-world conditions.