Since this thread is asking about the Pentax 67, I'm not sure that my experience with the Pentax 645 is germane, but here goes. I own the Pentax 120mm AF macro for that system, a set of extension tubes, (13.3, 26.6, and 39.9mm), and a Marumi 330 +3 diopter achromat in 67mm. I've printed "eye-sharp" 24x30" prints at 1.5x magnification using both approaches. On a copy stand, I typically use the extension tubes, but on a tripod I chose the close-up lens because the camera balance was better.
Originally Posted by Dan Fromm
I've used the 75mm f/2.8 with the short tube for some "near macro" work, as the 5.5:1 reproduction ratio of that lens can be limiting at times. Before I got the 120mm, I even tried all three tubes once. The results were reasonable, but I honestly feel the 120mm gives better results and is far more convenient to use.
So compared to a dedicated macro lens, whether you choose close-up lenses or extension tubes you're trading off convenience and some optical performance for cost. On "normal" lenses, I suggest using tubes. But once you reach focal lengths of 135mm or so, I suggest using close-up lenses instead.