GF5+14-42x vs RX100 for commuting/backup?

As others already said, it depends on what you mean by "backup".

For me the RX100 is the better "go anywhere" camera compared to any small m43 body and 14-42X.  Charging from USB is nice as you don't need a backup charger either.  Sensor quality is excellent.  Optically quality very good as well.  Buffer depth and speed are excellent.  I made a thin felt pouch for mine and it fits in a pants pocket easily - really can't do that with an m43 camera.  Focal range is sufficient for most travel/landscape/social shooting so lack of interchangeable lenses not too big a compromise as a "backup".

You said you were willing to go the extra mile to get a good 14-42x.  Be prepared to do the same with the RX100 - a fair number of units have had decentered elements in the lens.  So buy from someone with a return policy and test.  Keep in mind a 20MP you'll see minor decentering in the extreme corners no matter what, but a few users have gotten truly defective lenses.

The other mark against the RX100 is the price I suppose.  Not an inexpensive camera.  Also not like any other "compact" camera, the IQ is excellent.

I did still want a "back up" body for m43, and as my G1 was converted to IR and my GH2 sold what I did was pickup a $150 E-PL1.

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Ken W
See profile for equipment list