I don't know the specifics of the Xtreme Vision's construction, but it seems like Philips focused solely on making the filament as compact as possible rather than resort to a creative application of laser-etched blue tint (as with the NB Lasers).
While I can't say I've done testing as detailed as evo77, I can say that I've tested a few H11 bulbs with the same Stanley projector he used. I tested at the US standard test voltage of 12.80 volts instead of a more realistic voltage of 13.something volts.
I also tested with the Philips XtremeVision H11 bulb, which was missing from his test, and the Sylvania Silverstar Ultra H11 bulb. I hate the fact that no one who has any idea what they're doing has touched on the Silverstar bulbs. Yes, I know that they're terrible, but I also want to see just how terrible they are.
I've broken the data up in several charts instead of throwing it all in one chart to make it easier to digest.

The "Philips H11 (aged)" refers to the bulb that my Stanley halogen projectors came with. These projectors came out a used headlamp and were sold on eBay. The included bulb was a stock Philips H11 long-life bulb that was obviously pretty well-used, with a fuzzy filament (indicating a lot of redeposition) and slightly browned glass capsule (tungsten filament stuck to the glass). In other words: this bulb has seen better days. This is also the type and condition of bulb that most people are running when they complain "my halogens suck." All the other bulbs used in the comparison are brand new. Yes, I know I'm supposed to run the bulbs for 1% of their design life to "season" them to taste according to 108, but I'm not doing this for the government.
The new, Sylvania Basic bulb destroys the aged Philips H11 bulb at 1.5D, 2R. Yep, it's true, tossing out an old, long-life/stock bulb for a plain ol' new bulb can make a nice difference.
Okay, so far, so good...what about the other bulbs I tested?

The Philips XtremeVision at a mere 12.8 volts wipes the floor with the Silverstar Ultra.

The Sylvania Silverstar Ultra fails to differentiate itself from the significantly cheaper Sylvania Basic.
Okay, okay, make the pain stop! I know that we can overclock CPUs so that a cheaper CPU can beat a more expensive, non-overclocked CPU. Can we "overclock" the Silverstar Ultra so that it truly shines? Well, I tried running the Silverstar at 13.5 volts instead of 12.8 volts, and compared a 13.5 V Silverstar to a 12.8 Philips XtremeVision.

The Silverstar with 20% more raw lumens (thanks to running at 13.5 volts instead of 12.8 volts) still can't quite outperform the Philips XtremeVision.
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