Re: the difference between the old 6P bezel (round, Lexan window) vs. new 6P bezel (anti-roll, Pyrex window) that results in a slightly narrower beam with the new bezel
The new bezel uses a screw-in retaining ring that requires a sufficient amount of threads in the bezel's rim to fit the ring. Thus, the Pyrex window is about 0.13" below the rim vs 0.10" for the Lexan window in an old bezel. I can't tell if a drop-in also stands off farther from the bezel's rim because of different window thicknesses between Pyrex and Lexan.
One thing I forgot to note about the G&P bezel. The bezel comes with a silver ring that you can optionally drop inside of the bezel. The ring is essentially a standoff that helps push a drop-in rearward if it needs some slightly extra length to make electrical contact.
If you look inside of a standard SureFire 6P bezel (old or new style), there is a "ledge" at the periphery of the window on which the lamp's rim sits.
A G&P bezel has no such ledge. Thus, without the silver spacer ring, a drop-in's rim will press directly against the inside surface of the glass window. For something like a Malkoff M30, this might be an issue in terms of potentially scratching the front face of the optic. On the upside, the optional spacer ring gives you additional flexibility to adjust the bezel fit to reduce or eliminate any bezel-body gap.
I would imagine that the beam would be even wider without the spacer ring vs. with the ring, but my DX6090 won't function without the ring so I can't measure this.