Hmm.. i think that depends.. from what I can gather, the Leitz are apparently suited to BW photography and CZ to color. Leitz lenses seem to transfer better shadow details and tones to BW film than to color whilst CZ tends to do the opposite.
Well, at least it seems that way. I'm not that much of a hard assed photophile in that I would shoot and compare grain for grain /pixel for pixel. As long as I'm happy with the final product.. its good enough. That said, having gone through a hundreds of G-mount and M-mount images, I find that, visually, on color images, CZ lenses tend to produce warmer grey tones and thus make a picture appear richer in colors than the Leitz. Leitz on the other hand gives cooler grey tones thus skies tend to appear more vivid and deeper in colors. However, IMHO, I dont think it makes that big a difference in terms of color and IQ.. its individual preference and I think I prefer the warmer tones. Those ppl living in the northern and southern cooler areas may prefer the opposite.
If you can afford the Leitz and think it does give better color and iQ, then it probably does.. personally, I really cannot see that much of a difference for these two identically rated lenses and I doubt many people can either. I can however see a difference between my Canon Ls and the CZs in respect of color tones.. Canon's Ls produce a very neutral tone whilst, as said above, the CZs produce warmer tones.
RFs dont make money for me so I cannot justify a Leica.. even though I something wish I could.. maybe.. one day..

For the time being, I'm just so-in-love with the fact that I dont have to carry 12kg of gear with me and still make good leisure pictures with my new G2:bsmilie: