I've had a Pentax 6X7 for over 2 years now, with a 105mm, 55mm, and 135mm macro. This camera has such mixed reviews, but in my experience it is a fantastic camera. Think about it...Pentax did not change the basic camera for nearly 30 years, until they came out with the 67 II version in 1998. There's a good reason for that. It worked well and remained very dependable. The metered prism is extremely accurate...it averages the scene, which for most purposes does the trick. I'm sure with trasparency film it may be a little more finicky. I've recently started using a Pentax V Spot meter. Great meter, works well, but comparing my exposures, the metered prism was not far off at all. I only got the spot meter because I've always been passionate about the Zone System, and love working with black & white.
Great camera. I'm running a roll of film through it about once a week.