Oddly enough a few weeks back watching injectors flowing I didn't notice anything significantly different with siemens, still seen no improvements after people have swapped either, but each engine is different.
I would buy either different bosch or siemens, as greys no longer made, so if 1 buggered up you'd be stuck.
A car I recently checked the injectors on flowed evenly at around 42cc on a timed cycle, with VERY good spray pattern, the car in question was a 1.4 astra(gf's), it had a mystery misfire when cold, did all the usual no help, despite a very good pattern cleaned the injectors(thanks johno) and re installed could detect I thought a more even idle, thought could be imagination, but confirmed by all who've driven the car and the cold running has been helped no end, no longer has the sluggish cold performance, and no misfire in sight, like I say these looked very good to start with, checking after sonic cleaning showed a slight improvement, but was large benefit on car.
Flow after cleaning was around 38cc on same time cycle, but car goes noticeably better, they had obviously never been cleaned before, took nearly 45 minutes to coax them out, talk about stuck, maybe time to get injectors cleaned prior to new chips etc ?
tabetha