These responses are great! On the FABULOUS Zeiss images website that another member posted (
http://www.zeissimages.com/ ) the shots taken by Canon 5D seemed a bit 'punchier' and more 'detailed' and a tad 'contrastier' than many taken by the Sony A900/A850, which is what prompted the inquiry.
I became a fan of Zeiss when I owned my beloved Contax 139 (with a superb kit of glass that included the 25mm f2.8, 35mm f1.4, 85mm f1.4 and the 180mm f2.8 optics) and have been a big fan of Zeiss' magical 'bokeh' (which were equaled or occasionally surpassed by Leitz Noct and earlier Summicrons for the M cameras). No doubt the ZE designs have the same 'feel' as those for the Contax (albeit modernized to work on the Canon EOS body). The ZA's seem to have that magic.
Now part of the differences could be resolved in post using Lightroom and other fine software. And, it could also be that the Canon users on the site were a bit better than the Sony users. (I don't want to make any generalizations here just that it's possible Canon, due to it's longevity in the biz probably has a more talented user base than Sony at this time.)
No doubt the Canon 5D MkII is an incredible picture taking machine. And lower noise at higher ISO's is significant. My own approach in the digital age has been one of shooting color at lower ISO's (usually 100-400, 800 tops) and to deal with issues of noise at higher ISOs by simply shooting in BW which, in my opinion, even in at noiser ISO's has a more 'romantic' film quality about it that IMHO is FAR better than film was when it was available at those ISOs. The Dynamic range of the Sony at lower ISO's is almost legendary and the banding issues for the Canon 5D have been noted. (Athough I'd heard that Canon had a fix for that or am I mistaken?)
The issue of manual focus is also not insignificant. Canon provides a bright VF. The Sony is even brighter. The Canon has a fine micro screen available (EGS?) that would be worth looking into (literally). A company called Haoda (
http://haodascreen.com/default.aspx ) has some INCREDIBLE after market screens that rival the legendary Beattie screens may be even better. Plus AF confirm is a nice plus. All very nice.
But I find that there will be times when rapid focus will be in order and AF is nothing to be sneezed at. From time to time I do do events and AF is greatly appreciated. For most events, clients aren't all that fussy which glass you use for them as the results taken by either Zeiss or the best of Canon's own would not be noticeable in their perception. But there may times when I'm out and about and a rapid AF to catch a moment (although shooting Aperture priority to insure reasonable DOF will also work). In the end, AF is simply nice. (Sony's recent announcement that there will soon be a ZA 24mm f1.4 in their Zeiss stable could make it even nicer.)
Finally there is the matter of the menus. Sony's is far less extensive than the Canon but that may be a plus in that it is a lot less complicated. Again that's something that only use could answer.
The two systems I'm considering would be Canon's 5D MKII with ZE 21mm f2.8, 35mm f2.0 and 100mm f2.0 (along with the standard Canon 24-105mm for general purpose shots possibly mating it with Canon's 100-400mm f4.5 for those extra long shots a bit later). Or, the Sony A850 with the ZA 16-35mm f2.8 and the 135mm f1.8 (possibly adding the 24-70mm for general work and then the Sony G 70-400mm f4.0 for the really LONG stuff even later.
Guy, thanks for recommending that rental place in Memphis. They may be the best bet in comparing the two systems and what it would be like in real use.
And also for your kind words about my abilities that you'd seen from going to my website.
And again, thanks all for your comments that have been very helpful.