I'm going though mental convolutions at present about whether or not to stick with m4rds or change to a APS-C system.
Ironically, it is because of the Lumix 100-300 I am having these internal discussions.
The 100-300 has introduced me to the pleasure of photographing birds. I would not have been able to take a chance on a lens of this size with another system without spending double or even treble the purchase price.
Now that I've discovered how much I want to take forward this type of photography I have also discovered the limitations of the m43rds system. AF is slow, there is a single point of focus, metering is limited and sad-to-say anything shot at higher than iso800 has poor resolution. I'd say the high-iso issue is the most serious limitation. Here in the UK a lot of the time we are dealing with gloomy skies. The need for really clean iso1600 or 3200 shots is paramount. With bird photography cropping is essential and when you crop at above iso800 then I am afraid to say that on my GH-2 things turn to mush.
Unless, that is, I'm doing something wrong?
So, I am at a bit of crossroads. Do I stick with m43rds and limit my success with photographing birds, or do I change systems? The need to abandon m43rds is partly financial: I have a lot of money tied up in m43rds kit even at second hand prices and I do not want to proliferate my camera ownership into a 4th system. I don't think the wife will stand for it either!
It seems sad to ask for insights into personal decision making in a forum but a lot of people in this forum have more experience than I and have become virtual friends, so I would welcome your comments - no matter how critical!