Alright, I think I owe an update to all answerer to my post. I even almost stopped my "obsessive day dreaming"
In the mean time I bought a 5Dc, shot 1500 pictures in 4 weeks, and sold it with a nice profit last week. I was more than heavily excited by the pictures the 5Dc offered me. I F______ loved it! I even didn't miss the AutoISO of my 60D at all..
What's next? I will buy an used 5DII, because I don't want to use my 60D any more, after seeing what the 5Dc is able to produce. The shallower depth of field of my first full frame was enough to let me think no more about what kind of camera I want to shoot with. A FF camera comes very handy, as I own only primes, and none has a higher aperture number than 2.8. I also own two manual focus lenses, and only because of that I give a S___ about the antique AF system of the 5DII.
Maybe somebody is wondering why I didn't keep the 5Dc instead of getting a 5DII? Good question, I think it was because I want to shoot video occasionally as well, and the back screen of the 5Dc was just horrible. Also I couldn't hold myself back to sell the 5Dc with profit. Not to forget the lack of AFMA on the 5Dc (still the auto focus of my 5Dc was surprisingly accurate on all of my lenses..)
And yes, I got me a 135mm f/2 lens I was talking about. But not the "modern" EF one, but the old nFD, and already converted it to EF with the kit of Edmika. This happened this week, so I only had the time to go outside with it once (and only using it on the 60D) and honestly speaking, I am somehow surprised by the fair amount of CA. Accurate focusing with it is a another story. And there comes the second thing I liked most about the 5Dc, the large viewfinder! Every time I look through the viewfinder of my 60D now, I am just terribly disappointed. I am looking forward to use the 5DII (after I found one for a fair price) with my new 135mm f/2 lens! The converted lens has AF confirmation, but after my shooting I found out that it's not really reliable, a lot of shots where the AF point was blinking on the non moving subject turned out to be not sharp (at all). On my other converted lens the AF confirmation is much more reliable, and I am not sure why. I also tried the to use the manual focus lens with the ML focus trap feature, and it worked quite good, but it's not really helpful when shooting moving subjects (at least not for my shooting situations), and for non moving ones you mostly have enough time to focus.
One thing I am (or was) still wondering about, how much influence the pixel size has to the IQ of a camera? I know the 5Dc has the highest of all canon cameras! But after looking it up on the inter web, I guess everything above 4, or maybe 5µm makes no difference any more...
Thanks for reading, every further comment is appreciated!