Should I get a f/2.8 zoom?

My most used lens is the 24-105. I find the focal length to be extremely useful for my style of photography, as I shoot mostly in the 35-50 and 70-90 ranges.

But I have been considering upgrading to a 24-70 f/2.8 zoom (either the Tamron VC or the Canon Mark II version).

Low light is not an issue. Combined with the IS of the 24-105 and the 6D's low-light performance, I never find myself wanting for that extra stop of light.

Rather I'm looking for a possible increase in IQ (seems like a possibility in the Tamron, a definite in the Canon) and more creative options with the shallower DOF. Of course I'd lose the 70-105 range I like and the relative portability of the 24-105.

Considering this, would a 2.8 zoom make sense for me (and which one?) Or should I be looking at 1.4 or 2.0 type primes instead?

Honestly I would get a pair of primes to compliment the 24-105. The 24-105 isn't going to fetch much of the used market anyhow so getting a 35/2 IS and a 85/1.8 is going to run about the same for you and give you two stops at the focal lengths you often use.

That Canon 24-70 MK2 is just about the finest zoom lens ever made. Deadly accurate fast AF on top of killer IQ. The Tamron offers nearly the Same IQ...but falls short on the AF side.

The primes you mention do not have IS which seems important to you. They lack Zoom and will not have a practical advantage over the Canon 24-70 MK2 in IO. I think you have answered your own question.

I would also supplement your existing f4 zooms with primes. The 24-70 as great as it is only gets you one stop and if you are wanting the extra light or the backgrounds separation the primes will help.

I can vouch for the 24-70 mk II. It is one excellent lens.

The Dark Knight wrote in post #16694175
My most used lens is the 24-105. I find the focal length to be extremely useful for my style of photography, as I shoot mostly in the 35-50 and 70-90 ranges.

But I have been considering upgrading to a 24-70 f/2.8 zoom (either the Tamron VC or the Canon Mark II version).

Low light is not an issue. Combined with the IS of the 24-105 and the 6D's low-light performance, I never find myself wanting for that extra stop of light.

Rather I'm looking for a possible increase in IQ (seems like a possibility in the Tamron, a definite in the Canon) and more creative options with the shallower DOF. Of course I'd lose the 70-105 range I like and the relative portability of the 24-105.

Considering this, would a 2.8 zoom make sense for me (and which one?) Or should I be looking at 1.4 or 2.0 type primes instead?

Show us images where you feel the 24-105 IQ is lacking. Many times the perceived lack of IQ is more related to technique than equipment. I have some great photos printed that were shot with the 24-105. Now I do also have primes, but they are typically used in low light conditions.

You might consider a 70 - 200mm F/2.8 . I recently bought the Tamron 70-200mm F/2.8 with IC (they call it VC) and find it a good extension to my 25-105mmL. The 100-400mm is too big and heavy to lug around all the time (and pretty slow at its longest).

The Tamron offers shallow DOF when you need it, has a bit of extra reach over the 24-105, has excellent IQ and is about half the price of the Canon equivalent.

Hogloff wrote in post #16694435
Show us images where you feel the 24-105 IQ is lacking. Many times the perceived lack of IQ is more related to technique than equipment. I have some great photos printed that were shot with the 24-105. Now I do also have primes, but they are typically used in low light conditions.

Actually don't think the IQ is lacking in anyway. Some of my favorite pictures have come from the 24-105. I'm just thinking the IQ on something like a 24-70 ii will be even better.

I'm not a pro photographer, so I don't really have stringent IQ requirements, so there's no lens I own currently that I feel gives me "poor" IQ, even the cheap ones. I've gotten pictures I'm more than happy with every lens I own.

That being said, my 70-200 f/4 is gives me better IQ than my 55-250 when mounted on the same camera. My 55-250 gives me IQ that I'm happy with, the 70-200 is just better. So I guess that's what I meant when I said I'm looking for better IQ from the 24-70.