Originally posted by Squirrel am that guy who over researches and buys things with features I don't necessarily need because I read something on the Internet. So, I am just looking for some solid advice as to what fits my current needs and to what I can hopefully grow with. Lastly, I feel like I am looking for something to take quality photos that can focus quickly and track well when chasing my kids on the field.
Squirrel, I am very like you with the internet research, with the added issue that I am an Engineer, and so like to know all the technical fine detail. Like you I researched all sorts of stuff, and seriously looked at a whole range of DSLRs and Mirrorless Camera's. Cut to the chase - last month I brought a K-5, I also have a 55-300, and will get to that with comments below.
In my research I was looking for an APS-C, high IQ, interchangeable lens, relatively small camera (as I travel a lot).
As part of my research I was reading Luminous Landscape as we have some stunning landscapes near where I live and I enjoy photographing them. I saw several articles by Sean Reid, Reid Reviews which made sense to me, and in the end I subscribed to his review site - it is about USD $30, and well worth it. Sean has a very measured and in-depth review of the K-5, some mirror less and various other cameras including the Fuji X-Pro1.
One particular article on his review site was called 'Seeing your Subject' and was a look at using Optical View Finders verses Electronic View Finders. I found once I thought about it - it was a key issue for me. I really like using Optical View Finders. Once I made that decision, the field narrowed very quickly - Range finders, DSLRs, Fuji X-Pro 1.
The second article that had a large influence on my thinking was one by Thom Hogan on lens selection - lens availability is really important - I didn't want to be waiting for 3 years for 'roadmap' lenses to arrive. This is where Sony NEX and Fuji X-Pro 1 have issues - their current lens selection is limited. m4/3 and DSLR systems have much more mature lens selection - and Pentax K mount has lenses going back to the 1960's that still mount and are very usable on the digital bodies. Nikon also do to for that matter.
My selection criteria - with optical finder, good (and affordable) lens range, smaller size for travel, great IQ etc left me looking at the Fuji X-Pro 1, Pentax K-5 and Nikon D7000. The Fuji is only just available, and more expensive than the other two, with a much more limited lens range.
In the end the Pentax small primes, smaller body, and weather sealing (really useful when traveling - in a place for one day and it is raining) swung it to the K-5 for me.
I am very happy with the K-5 - it is a superb little camera, great price for what it is, fantastic IQ, meters old lens (cheap and fun to play with), very small with primes attached, and I have found it relatively intuitive and easy to use. I previously had a Nikon D200 - and the K-5 is way easier to learn/use than the Nikon. It is also significantly smaller and less bulky too.
In the end you need to work out your own selection criteria and deal breakers - the Optical View Finder vs Electronic View Finder was one of the key ones for me.
With regard to the 55-300 and your comment regarding speed - please remember that this type of lens tends to get used outdoors, especially at the long end - so low light (mostly) should be less of an issue. The K-5 had shake reduction that gives you a couple of stops straight up, the K-5 also has high usable ISO that also gives you more range - so.....please bear that all in mind when considering how you would use the 55-300. it is a very nice lens for the price.
I hope all this helps
Ross