Wow, some of the smaller used bodies are cheap! They should be cheaper than the NX300 since the sensor cannot keep up, I'd expect.. but checking online shows me the excellent Sony 4/3 sensor is in the ePM2, the same one that the EM5 and later models use. The ePM2 is (slightly) smaller than the nx300 and takes telephoto lenses that are far smaller than the APSc sensors will allow. Interesting.
Personally I've viewed Olympus Pen (really all their cameras) with a jaundiced eye (whatever that is, why does a yellow eye make a difference?) - my thoughts align well with this New Camera News post. How would I choose a P/PL/PMx (where x=1 to 5) and know which feature-set I had, or didn't have? The EM5/10/?? feel the same way. Too many similar-looking cameras with discontinuous numbers and letters that fail to convey how things differ. Ugh.
I have always entered the µ43 system through the Panasonic door, and never the Olympus. The Olys have in-body IS like the Pentax bodies, so you'd think I would have tried one by now. The confusion above was one deterrent, the appeal of the Lumix bodies another. But given the NX300 currently in hand why should the Olympus bodies be shunned? My NX300 plus 20-50 lens has no IS at all, and to acquire an IS lens would cost more than the PM2. Interesting again!
The PM2 is set up as the 'entry' Pen body, and with no mode dial it seems pretty crippled. But it has a touchscreen and control panel similar to Pentax' Info-button screen (and the NX300 one too) which makes many functions easy. I'm liking what touch screens offer on cameras, both as an alternative to buttons & dials plus the ability to AF on demand to a specific location. So the leaner option is as good image-wise as the beloved OMD EM-5± and can take lenses that will fit better in a large pocket or small rucksack. That's a good thing.
The down-scaling that comes with making a lens cover only the 4:3 sensor allows for a smaller 100mm lens, and it produces images that print like a 200mm (or a 150mm on APSc), so less actual telephoto mm yields bigger results. That's another good thing.. and add the really low price for 'strike three'.
I'm not planning to do a major dump/rebuild.. but I might dabble a bit. The price is low enough that, whatever the result, the 'rental' cost would be pretty low.
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On the Pentax side, I'm letting the HD55-300mm WR lens go. Crazy again, but that's the 4th time I've done that so it's not a huge surprise. I own both the Quantaray 100-300 and a Spiratone 300mm mirror lens, and all three around 300mm look interchangeably similar. So I'm swapping the HD for a WR 50-200mm, which is much smaller and takes smaller filters. This will clarify when to carry which big lens, since I had so much overlap above 200mm. It also brings cash back into the system, which can be used for the 'dabbling' above!