James....congrats. ....and I am sorry.

I am glad to hear you like the 5DIV so much. The 5DIII is already a remarkable camera and it seems Canon made many improvements for the 5DIV.

Regarding lenses. If you loved the 35 L II on crop, I would really think about 50 mm. You could start with a less expensive and very capable 50 f/1.8 or 50 f/1.4. I've owned both. I found the 50 f/1.8 to be remarkable from about f/2.8 on, but it was the AF that lost me (which is now improved). I upgraded to the 50 f/1.4 and was very happy shooting it from f/2.0-2.2 and up. Crazy good sharpness. But I decided I wanted more sharpness down to f/1.4 and got the Sigma. Bigger, heavier, but a remarkable piece of glass.

Granted, it sits a lot as the 24-70 II is on my camera pretty much all the time.

Regarding your dilemma, let me assure you, it is a real one. I have starred at and pixel peeped enough images to have convinced myself that I can see a slight improvement with prime lenses over the 24-70 II. But it is very slight with the most significant difference being vignetting (and associated adjustments in LR) at f/2.8-f/4 (other than having f/1.4-2.8), distortion, and I also like the "rendering" of primes a bit better in some instances.

But, are those slight differences worth the investment in a full prime lineup? Honestly, I can see people going either way...prime or high end zoom. I think both groups will take some amazing images. I think the high end zoom will be for those that want to ultimately pay less and prefer convenience, less weight and flexibility. For those that go with a primes, I think they'll ultimately spend more (~2-3 primes vs 1 zoom), packing the kit will take more room and weigh more, but there will be a slight benefit in IQ and they'll have apertures faster than f/2.8.

Both great, just different.

As for me and the way I shoot.....the convenience and portability of high end zooms far outweighs the benefits of multiple primes. So I have taken to a philosophy of basing my kit on high end zooms and supplementing with primes where there is a definite need.