K1 v K5iis

I did this upgrade but honestly can't answer this question because "performance" is such a broad definition. It's a lot quicker in use if that's what you mean.

yes

It's a big step in various ways, so absolutely yes.

From a K-3 to a K-1 would be a different issue.

It's not so much that as them being very different propositions. For example, the K-1 is superb, but full frame lenses will cost serious money and are big and heavy. By comparison, the K-3 is smaller, lighter and we probably have the lenses to go with it. So there are all sorts of factors apart from quality that come into it.

Sue bought a K-3 because she wanted the pop up flash and it was the right weight for her. The K-1 was too heavy. I bought the K-1 because I really liked the lenses and the camera. Having reviewed the lenses for EPZ I didn't want to send them back, but back they went and I bought the camera and the 28-105mm for starters. Next up will be the 15-30mm, but it's more serious money and will have to wait for now.

Of course, if the truth be known, we both fell in love with those cameras at the NEC and simply wanted them. There's nothing wrong in wanting things.....

You're right to seek the opinions of actual users (after the initial excitement period is over) as it's the little comments and notes that often reveal how much of a difference there is for the particular fields of photography that we each do. I rarely shoot any action stuff (Birds, Motor sport, etc.) so the advances in AF response would make little difference to me, but the appeal of using Full frame lenses and benefiting from the depth of field make it quite tempting.

Ive not used a K1 yet. But having seen the reviews. Its not much of an improvement in performance. So for the exercise of shooting birds I too would say its a no...

In day to day use the K-1 is a nicer camera to use than the K-5 IIs. The interface is very responsive, the third dial is very useful as is the screen. Obviously the viewfinder is bigger too which makes MF slightly easier though I personally never had any trouble with crop cameras.

Honestly though: the biggest difference is lenses. I already had a lot of FF lenses so there wasn’t much adjustment in gear perse. But every lens now has a different rol. On crop I used my F28 a lot, the FA43 has taken that role, which used to be a wide portret kind of lens on crop.

I do slightly miss the DA 18-135mm which is smaller and has more reach than the 28-105 on FF. And looking to replace the DA50-135 I’ve come to realise how compact it is compared to 70-200mm lenses that are available.

On the other hand, none of my older Pentax glass has disappointed, quite the opposite actually. The FA85 is obviously fantastic, always a bit too tele on crop but now back in its true role. But also modest lenses like the A50 Macro are surprisingly fantastic on FF.

Personally I enjoy the shallower DOF FF provides but I can say I’m taking better pictures now. Also there are a lot of great deals on secondhand Pentax DA lenses.

And regarding the physical size and weight: you get accustomed to the larger size and weigh very fast and I don’t have a crop DSLR any more so I’m not reminded of the difference. The excellent grip it has helped adjusting too. I thought I would use my K-01 more for the smaller/lighter package it provides but I’m still in a honeymoon mood and take the K-1 everywhere I go.