I have a 5D MkI, but I prefer a 30D for studio work, but when I get a 85mm portrait lens, I'll probably retire it to backup. I use filters on the strobes to calm down the skin tones. I feel they are a little bit on the cold side with digital, especially older cameras.
A lot of prosumers and retail photographers fail to appreciate the original 5D. The old "gotta have the newest thing" syndrome. A lot of us feel the colors are truer than the software of the MKII and III. If the II hadn't had movie mode, most probably wouldn't have bought the hype and replaced their MkI. If I get another FF body, it will probably be the 6D.
The Pen has warm skin tones. Very complimentary to the subject. Unfortunately, the IQ isn't up to my standards for some other work. Of course, that may just be me figuring out the different format. But, as I said, the truth is in the prints. I have a feeling that an 8x10 will be fine, 11x14 might be passable. Anything larger....who knows?
When you posted here before about what camera to buy, I said then if I could shoot weddings with a Pen, I'd do it. Customers just expect that big ass, heavy DSLR. Otherwise, they believe they are getting cheated. I asked customer once if she wanted any B&W for her daughter's wedding. I had to know up front, because B&W was (and still is for me) hand processed and more expensive. If she wanted any B&W, I had to increase the price. Her reply was to accuse me of trying to cheat her by using black and white instead of color film.
It was that kind of attitude that took me away from retail photography and more to commercial photography.