60D:
- I keep my shots at ISO 800 or lower if possible.
- If absolutely necessary I bring it up to ISO 1600
- ISO 3200 is too grainy for my taste
5D3:
- Normal limit is at ISO 3200 for me
- In dire situations, ISO 12800 is still usable
In your case, the 6D should be better at handling noise so the 5D3 should be a close comparison. The settings also depend on what you shoot and for me, I tend to follow certain settings depending on what I shoot.
Portrait:
- I keep ISO at 3200 or lower to make sure there's enough detail
- Aperture is usually 5.6 or wider for me depending on what I'm trying to get
- If available light isn't enough, consider using external lighting (not always possible)
Events:
- This is where I usually have to sacrifice ISO. Just get it as low as possible.
- Aperture usually stays between 2.8-4 (on my 24-70 zoom) for individuals and it can stretch to 5.6 for groups (again, the limits depend on what you're trying to do)
- Consider fill lighting if possible
Landscape/Cityscape:
- LOW ISO! I stay at ISO 100-200 for this one
- Longer exposures + tripod is usually the best solution unless you don't wan't trailing lights at night
That's me of course - and photography is just a
really expensive hobby for me. Others might have other preferences.
On your 28mm, it doesn't take much to not have bokeh (assuming you don't shoot your subjects in front of their face

). I don't personally own one, but at 24mm, I get less bokeh starting f/4 (or even f/2.8 ) assuming I'm far enough from the subject.