Quote Originally Posted by Paul Sorensen
My primary camera is a Mamiya 645 Super and I love it. The newer Mamiya 645s (the Super nad Pro series) have interchangable backs and the lenses are super cheap. Telephoto is not a really strong suit of medium format, mostly because the lenses get huge and expensive. I had a 210mm for the 645 and it was a very nice lens. It sells at KEH for well less than $150 in excellend condition, so the prices have become very affordable. The Pentax 6X7 is also affordable right now, but it will likely cost somewhat more. It also weighs a lot more and is more difficult to hand hold. I don't know all that much about the Pentax 645, so I will leave that discussion to others.
Reading this thread prompted me to open a book I had obtained secondhand several years ago in Hay-on Wye in the UK called "Great Action Photography" published in the early 80s. It is a series of photos and interviews with action photographers.Most were using Nikon with one Nikon to Canon convert. Interestingly two of the German photographers were using Pentax 67s.

I have only seen a Pentax 67 on a photographic shop shelf and never handled it but it did look a monster in comparison with 35mm but clearly it must be manageable for handheld action shots. These were photographers who actually chose to use a 67 as opposed to 35mm. Of course wandering around all day with one slung round your neck may be something else again but it just struck me that a tripod may not be essential.

Incidentally for those based in the UK and interested in photography books both new and secondhand it makes a good day trip. Scenery near by in the Wye valley isn't bad either.