For studio shots, the ISO 50 works awesome! I can now dial in a very wide aperture even when I'm using studio lights which overexposes a shot when you are using ISO 100. I have used a mamiya at work and it was the first camera I've used which has a minimum ISO lower than 100...and it was perfect for studio work. Since I cannot afford a 15 thousand dollar camera the 5d mk2 is good for the price. The lower flash sync speed which is 200/sec doesn't really bother me. I rarely use a speed above 125/sec in the studio anyway.
I basically tried out every lens that I have on it. Pretty much 2 of my lenses stood out on the 5d. The mighty 70-200 IS USM is phenomenal with this body. I have been using it with my 50d but the results with the 5d is unbelievable. I cannot believe that I wasn't using its full potential with a cropped body. Another lens that blew my mind away was the Canon 50mm 1.8. The 50mm was the biggest surprise of all, considering it was under $100, it had the ability to showcase the full potential of the full frame sensor on the 5d. If only the 50mm was a macro, can do wide and telephoto, then I would probably just glue that thing onto the body.
Doing shots for stock photography sites, the 5d is the perfect camera for me. The images that it produces basically have a lower noise level than my other bodies...exactly what I need for stock photography sites. I really didn't wanna spend hours applying noise reduction in some of my shots. In real life nobody really looks at photos at 100%. With stock photography sites, everything is looked at a 100%. Even that hair on your cupcake shot that is only visible at 100% will break your photo. Having less noise straight out of the camera is a real nice perk from having the 5d.
I haven't tried shooting birds or sports with it though. But that'll come later.
All in all I can say that it was really money well spent!
I can say proudly that these images were NOT sharpened in photoshop...also these have been converted to jpeg format. The original shots were 10 times better!