Does the the filp out screen really make a difference?

You haven't said anything about how you will use the camera.  Will you be shooting outside in rainy and dusty environments?  Go for weather sealing.  (note: the lens also needs to be weather sealed)

Will you be taking lots of shots from ground level or up above your head or pointing back towards yourself?  Go for a flip out screen.

Going solely by the comparison stats, the Pentax looks like the better camera.  There are no DxoMark scores for these yet... but they have the same size sensor and the Pentax has smaller resolution -- so it probably has the better image quality.  Also, it has a larger viewfinder which is a nice to have.

I recommend that you use Pentax, because it is much cheaper, and the picture quality is so GREAT! especially with image quality. My cousin has one, i loved it. The tilting screen is not a big difference. its a good use for self portraits, but with DSLR's now and day, we let other people take our picture.

Is the flip out is worth more than the the weather sealing? Not for me. I have a camera with a tilting screen and for sure it can be useful sometimes, but only sometimes. And even if you don't plan on running in the rain with your camera, Pentax is simply better protected, so you don't have to worry that much. Plus Pentax has much more features.

I personally think that flip-out screen make some differences, though not that much. 

With articulate screen, you can take self-portrait pictures of yourself and others. Also the flexibility of the screen will help to take picture in tricky situation  

Weather sealing Nuff said..........

Flip out screen has no real purpose I think....

i have looked aroud th tree of these camera. whan the k-30 takes a photo the movement of the miror actualy makes the camera shake a bit. so i choose the 5100 in which tou hear the miror but do not sense ant mouvement. plus its much cheaper even if it was the camera of 2011 of many review site