First, the lenses do make a huge difference. Coming from a tech cam shooter that had the 40HR on my Cambo, there was not much that could compete with it.
Second. It is not only a comparison of the Pentax against the Alpa but what back is the Alpa using.
Many many reviewers on the net consider the sensor in the Pentax to be one of the finest on the market (especially for the price point as you are roughly 1/3 the price of the Hasselblad and 1/5 the price of the Phase kit), but again, that is a matter of personal taste.
If you prefer to shoot with a dslr body, then the Pentax is an extremely good choice as your latitude is great considering that it is equipped with the Sony CMOS sensor (the same as in the IQ 250, 350) The one drawback is that Pentax do not have a sizable stable of lenses that can keep up with that sensor, but you can use the Hassy V lenses with an adapter.
On the other hand, if you like the versatility of being able to shoot with a DSLR or a tech cam, then the Pentax won't work, unless they come up with a way to mount it to an Actus (which to me is not quite the same thing).
Lastly, it is difficult to compare jpegs from two different processing software suites as each one uses its own algorithms to do the work.