Sounds to me like the A55 might be better suited to your overall needs, notably because video is fairly important too. IQ wise, there's likely little difference between the KR and A55 for most shooting. Though they are indeed using Sony sensors across the board now, oddly the KR sensor was a slight step different from the KX, which used the same 14MP sensor as the Sony A550 & NEX series. The KR uses a 12MP Sony sensor, which isn't currently in use in Sony's own lineup...it is likely some evolution of Sony's 12MP sensor from the A500. It's a fine sensor, so no problems...just wanted to point out that the A55 has moved to the new 16MP APS-C sensor, which Pentax uses in their mid-level K5. So the Sony will have a resolution advantage - and high ISO performance is probably close to a draw, with the A55 sensor performing a little better, but losing a little bit of light to the pellicle mirror.
Unless you have any issues with the smaller body size or feel of the Sony, it would seem to be better tuned to a combination of fast still AND good video performance, so seemingly the better choice. I can't imagine the Pentax KR having any still image advantages (The more expensive K5 would probably be a bit better than both at higher ISOs), and the Sony has a clear video advantage.
Sony DSLR-A580 / Sony 18-250mm / Minolta 50mm F1.7 / Sigma 30mm F1.4 / Tamron 10-24mm / Tamron 150-600mm / Tamron 90mm F2.8 macro / Minolta 300mm F4 APO
Sony A6000 / 18-55mm F3.5-5.6 / 55-210mm F4-6.3 / 10-18mm F4 / 35mm F1.8 / 16mm F2.8 / via manual adapter, lots of Pentax K mount, Konica K/AR mount, and Leica M mount manual lenses