Canon 16-35mm f2.8 II vs. Sigma 35mm f1.4 - for concerts & weddings

I realize these lenses are different. In a perfect world I would have both. However, money talks - unfortunately. I shoot a handful of weddings each year, and have recently been getting into concert photography (as well as general portrait stuff, and race (running) coverage).

Currently, I have the Sigma 35mm f1.4, and it is awesome. Very please with it, even compared to the Canon L (as I know is the general consensus, especially for the money). I've tried both and prefer the Sigma. I also have the Sigma 50mm 1.4 (one that actually focuses correctly) and Canon 70-200mm f2.8 IS II. I do have a Canon 24-105mm f4 IS, but I am trying to convince myself to shoot prime and at higher apertures more and more. I recently shot a complete wedding without it, with the other lenses in my lineup and with a rented Sigma 85mm f1.4 (which I intend to purchase in the coming year). I currently shoot with a 5D Mark II and a 1D Mark III (plan to upgrade to a 5D Mark III this year).

Anyway, enough with the boring story. I do have a need for pretty wide shots sometimes, especially with the concert and event coverage stuff. For a couple hundred more, I could swap out my Sigma 35mm for a used Canon 16-35mm II. I realize the difference in aperture. I typically use the Sigma at f1.8 and up, however, it is pretty usable for me below f1.8, if necessary. I did notice some difficulties with the Sigma while AI Servo tracking at this most recent wedding. I am assuming that is something that the Canon would excel at. Also, the ability to maneuver in that 16-35mm range would be handy. I could recover the need for shutter speed by bumping up the ISO if necessary. If I'm in a complete jam, I'm thinking I could swap out to the 50mm and just re-position myself, if possible.

Just wanted to get opinions from others. I'm good at rationalizing and talking myself into things

I think you've got everything. At least for weddings. (I don't know much about stage photgraphy.) You must have strong neck and shoulders to carry all that stuff: 2 FF bodies, 70-200 f2,8, 24-105 f4, 3 Sigma heavy primes, and I suppose at least 2 flashes, batteries, light modifiers and more.

The 2 zooms can cover the action (when you are restricted in moving) on the weddings. Flashes (still bounced) mostly on shoe to remain mobile.

When you can control your shooting postion (wedding couple portraits, candids, guest portraits, etc) take the 3x 1.4 primes for beautiful bokeh, and the serious lighting equipment if needed (multiple flashes off shoe, soft boxes, etc...)

Yeah, the wide angle is very nice sometimes, but you have 24 mm. The focal length is not the complete story. You can help much more the quality of your photography with properly planned lighting.

BTW: I work with 3 primes: 24L, 85L and 135L.
--
Yours Truly,

sempervivum