I use the Pentax 6x7 and 67II with 45, 55, 75, 105, 165 and 200mm lenses. I used to have the 90 and 2x converter as well, but got rid of them.
I find this system to produce images just as good as my Hasselblad, but as it has 6x7 negs, they actually produce better images at 16x20, because there isn't as much cropping and enlarging that takes place. I bought this camera to do a photo documentary for 8 months, but also used by Hasselblad. I found that most of my images were used from my Pentax 67 kit. It's severely underrated in my opinion and have the 4000 dpi scans to prove it. The "mirror-slap problem" is highly exaggerated and the system if half the price. I'll keep both systems because they require different styles of shooting and produce very different images, but I use both equally and rely heavily on the Pentax 67 for phenomenal quality.