Originally posted by clackers The pixels *aren't* bigger at all.
Less downsampled? We need a vocabulary to be unified and widely adopted to describe these things.
By way of example, here's the same photo three times cropped more and more,with the dimensions of the crop listed below (in pixels:P), then downsampled to a common viewing size. The crop at each jump is approximately 2x, compared to the 1.5x crop from FF to APS-C (so more extreme). This is iso1600, 1/250s out of a k5iis (and not starting with the full sensor image in the first place).
Noise reduction in LR turned completely off.
The moral, to me, is given a fixed output image size, the more you crop the more noise becomes objectionable (with the caveat that you might be able to do a bunch of cropping before you even notice any noise at all). A side-moral is that even the 5+ year old sensor from the k5 series is pretty darn good (and would look even better with some noise reduction), so having to crop your K-1 down to a k5 level of performance isn't going to make you cry.
If it was me with a K1, I'd keep my APS-C lenses until I got around to buying suitable FF replacements then sell off anything redundant (this is assuming no APS-C body is kept as backup). That K1 has an extra enhanced k5-series hiding in it, and there's no reason to be shy about using it in the interim, or even long term if you have an aps-c lens or two that you just love.