I defer to those more knowledgeable, but...
I love the Pentax 6x7, but felt the ground move on occasion when the mirror slapped back down. MLU (mirror lock-up) is a must if you choose this system.
I've owned and gotten some great images with the RB67, and it never let me down, but (and this is big) it hurts your shoulders after a while trekking over hill and dale, especially if you carry a couple lenses.
I actually went to a Super Graphic system, with grafmatic backs, which was actually lighter than the RB67 with a couple lenses and backs; the lower sharpness of the LF lenses was made up for by the bigger neg; so that was a good alternative for me.
Frankly, you should also consider Hasselblad (way cheaper than years ago), Bronica with PS series lenses, perhaps a Rollei SL66/SLX, or even an Arax/Hartblei (Hassy copies) system. Most of those systems have price stabilized, so buying one and re-selling later should not hurt your pocket more than the cost of shipping... and of course, rental is a great idea.
Any way you slice it though, the big difference will be neg size, not overall sharpness...compared to 35mm.
If you ever do consider rangefinders, you really can't go wrong with the Mamiya 6/7.
Last edited by dhosten; 12-01-2010 at 08:01 PM. Click to view previous post history.
Reason: forgot to add the Rollei option, and links