Two 6X7 Pentax systems have come and gone at our house. There won't be a third. I love the idea but I hate the execution. They are unweildly, heavy, and the mirror finally slaps so hard it just about tips the tripod over. They are nearly useless for hand holding. The one exception is to use an L bracket and do every shot with a Vivitar 283. The optics are really very nice and priced fairly on Ebay. I once tested my 165mm P67 lens next to a Konica 150. Under a loupe the Konica seemed quite better. And they're nearly worthless on the web. As with all my opine's, YMMV.
The second of the 2 systems I bought to take photos of my grandbabies while they are small. $1500. I replaced it with a $65 Minolta Autocord that is light as a feather around my neck.