it's worth what you want to pay for it.
Some other points to consider:
the xpg (as an emitter) is actually cheaper than the xre's that preceeded it (which has been awesome for anyone who consumes emitters).
While the xpg is more efficient (longer run time) 105 lumens is really at the low end of potential output. At these low drive levels, are you getting much gain?
Can your eye tell the difference between 90 and 105 lumens (usually not).
Big issue is beam pattern, tint. Some great Q5 bins available, so you could get really nice tints. Conversely, the xpg, as stated may be pleasingly more floody, will have (marginally) less throw, and likely a greenish tint (very few xpg's have 'good' tints as of yet)