in a recent autoexpress test with 60 bulbs, 2 bulbs came out as their top choice for bulbs that offer 50% brighter compared to standard bulbs.
they are 1) Osram Silverstars 2) Philips VisionPlus
here is what autoexpress said about them
Osram Silver stars
Beam: 96.9m
The flagship bulb in Osram's bulb range, the silverstar's 75m figure was only a fraction better than that of arch-rivals Phillips, but it performed significantly better at 50m. Add a price advantage, and the Osram's plus 50 per cent competitor is our best buy
Philips VisionPlus
Beam: 95.1m
It's behind Osram's finest but Philips top-of-range option is superb bulb which performed comfortably ahead of the 30% premium versions, You can not ignore that performance, which is why the VisionPlus merits our recommended award.
I have personally tried these two bulbs and can highly recommend them as
there is definately difference over standard bulbs. Although I have not personally tried PIAA bulbs but autoexpress does not give them a very good rating in their test.