Whatever you choose, Pentax or Canon or Nikon, get two of them. Malfunctioning equipment is no excuse for not getting the shot.
Until recently, I've shot with a Pentax K20d + DA* 16-50 and a K-x + DA* 50-135 along with a Metz AF-1 58 flash. I usually had a fistful of primes in the bags as well (21, 40, 70) just in case one of the zooms packed it in. My only single point of failure was the flash; knowing the K-x could shout print-worthy ISO3200 made me confident that even a busted flash wouldn't stop me.
The K20d was very good except of the AF. The K-x was very good except for the lack of two e-dials.
For photojournalism, having 2 bodies is much more mission critical than FF or the name on the body.
Some examples:
K-x with DA* 50-135, ISO1000:
K-x with DA* 50-135, ISO1600:
K-x with DA* 50-135, ISO2500:
K20d with DA70 F2.4 Limited, ISO2500
K20d with DA* 16-50, ISO1600: