From my research, and from what I gathered, so this is to my knowledge, not from a spec sheet, the nozzles are the same size between a BEW and a BRM. The difference is the size of the plungers.
BEW = 8mm (putting them in a BRM is a slight upgrade)
BRM = 7.5mm (putting them in a BEW would make it run poorly)
BRMs are a different animal in hardware setup. For example the turbo, intake, intercooler setup like Oil Hammer explained, and explained very well. From research, the BRMs have much more tuning capability, and were able to afford the use of a smaller plunger, albiet a half of a millimeter. The cooling setup, difference in ECU tuning, and all other differences adding up, including increased size and weight of a Mk5 over a Mk4, and evolving emissions, deemed them to use smaller.
I feel if you put BRM injectors in a BEW, you will starve it for fuel, bringing the map out of spec, and needed to ADD much more fuel via the ECU to meet the demands of the turbo, and EGT temps. This is only specultion, but you could possibly make your 100hp BEW a 90hp BEW.
For my BRM, I have a set of BEW injectors, freshly serviced with new DLC-800 nozzles installed by DBW LLC. I'm looking forward to this as a nice upgrade in MPG and power. They will serve well with the GTB1749V turbo I plan on installing before the end of the year.
The upgrade from BRM to BEW injectors is slight, but an upgrade altogether. PD150 injectors weren't sold on me due to the indirect design, and the lack of range in tuning they offer over aftermarket nozzles.
This is my 2 cents, and I'm waiting on the injectors to be installed. I'm fully turboback 2.5", all deletes, Frank06 stage 2 cam kit, and a 6-speed trans from a BKD. I'm ready and in need of the extra power and MPG.