Panasonic gx1 or Olympus E-PL5? Backup to OMD

Shooting RAW and tweaking in Lightroom should allow you to easily harmonize the GX1 and E-M5 outputs in post, especially if you profile both cameras using a color target. Shooting JPEG would be a little bit more challenging to match the outputs.

I use both the GX1 and E-M5 and I'm of the opinion that if you take a day or two before hand to get used to the GX1 interface (relatively simple compared to Olympus), you'll have no problem using the two cameras interchangeably. I've owned m4/3 bodies from both manufacturers, and though I prefer the interface and AF implementation of Panasonic, I can work Olympus cameras just as instinctively.

Also, if the E-PL5's IBIS is anything close to that of the E-PL2, then IBIS won't much of a selling point, because I didn't find IBIS Lite to be very effective.