what the X100 & X-series offer that other mirrorless don't.....

Having a Canon 5D2 a X100 and a XP1, my feeling is that the X cameras produce a better per pixel rendition leading to very crisps images especially in landscape, foliage

They also produce nearly pefect OOC JPEGs that will liberate some hours of your free time to practice more photography and less PP in front of your loved computer...

The way you can adjust the tonal curve for OOC JPEG is marvellous with both DR adjustment and shadows and highlights adjustments

And the high ISO performance is amazing noise being really a problem after 6400 iso and only for A4+ prints

This leads to 13+ EV DR in OOC JPEG If you add the Fuji color rendition, here you are!

In my knowledge the main challengers Sony and  Oly do not produce as good IQ as the Xs Fujis, but they also have very strong criteria for the choice...

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Good judgment comes from experience
Experience comes from bad judgment