Great answers!

Here is my advise: do as Ben suggests and shoot the 124G until it is worn out. I did that with a Vb many years ago - on tripod for landscapes, on monopod for "street", and handheld for very little. Cropping to 645 aspect is easy and can be done in both directions with equal ease. (BTW, the monopod and a lens hood were my two most valued accessories.)

Suggestion: invest in film and travel. Stop thinking about gear!