Bottom line.......Through all the good, bad, and ugly there eventually evolves the truth. You can find it here if you just look around a little. The truth is that the K5 is no doubt the most loved DSLR Pentax has ever made. It is a Game Changing winner, and nothing else comes close to it at anywhere near the price. Even those with some problems still want it...because it is that good, no kidding.
Your odds of having a problem are tiny, very tiny. Your odds of missing out on a great camera for your trip if you skip the K5 are enormous.......sure, the D700 or D3X will certainly equal it, and if you can bring along a good forklift to carry them, you will still be just as happy....maybe?
This is not rocket science, the K5 is a superb camera, it is well documented here by the many, many satisfied users, by independent tests all over the internet, and by you when you get one. Life is short, get a K5 and enjoy more of it!
Regards!