Looking at it from the other point of view, what is it that you like about your primes? If it's shallow depth of field, then getting a 24-105mm f/4L doesn't make much sense! If you find yourself stopping the primes down to f/2.8-4 all the time, then the only reason to have primes instead of a standard zoom would be to force you to think about your framing and perspective; a zoom is the opposite if this too. So I would ask yourself again, if you like primes so much, why

Might I suggest that if the 5D MkII and the three primes that you have are too heavy and bulky to carry in certain situations, then a 5D MkII and 24-105 f/4L IS won't really solve that problem. If this is your thinking, then have you considered a mirrorless camera with the equivalent fast primes to your 'L' collection?

*do*you want a zoom?Might I suggest that if the 5D MkII and the three primes that you have are too heavy and bulky to carry in certain situations, then a 5D MkII and 24-105 f/4L IS won't really solve that problem. If this is your thinking, then have you considered a mirrorless camera with the equivalent fast primes to your 'L' collection?