Hrm... so some thoughts for you perhaps.
17-40L - If a lot of your shots are at 50mm, have you considered how 40mm isn't much different? As long as you don't move closer to subject, there's no distortion (distance being the same) from 50mm, so at worst, you simply crop a wee bit to make up for the framing of composition. It's plenty sharp stopped down, as I assume you're shooting studio, and it's a very useful wedding lens as it is for groups. Not a heavy lens at all. Just something to think about really.
Tamron 45mm F1.8 VC - Basically a stabilized 50mm. The only one there is on the market for Canon. Very sharp, still quite fast if you need that, and of course, stabilization. It's half the weight of those F1.4 gems. And really, you'll be stopping down, so aperture isn't paramount. You'd be hard pressed to see a real difference at F2 and F2.8 between all the major current 50mm's. So, the benefit here is weight & stabilization, to which it has no rival yet.
Canon 50mm F1.8 STM - Cheap lens. If you know you want 50mm, and you're shooting stopped down in studio, this lens is nearly indistinguishable from a far more expensive lens at F8. Super light weight. So cheap, who cares? Just being real about shooting F8 when comparing $1k and $100 primes, as there's very little difference honestly.
That said, most people are going to focus on the wide aperture, bokeh properties, etc, but in your business, you're usually using lighting and stopping down a bit if not a lot, so I imagine F1.4 isn't really a big deal to you? If that's the case, and you're stopping down, this really levels the playing field for a lot of these costly and heavy lenses, as you really will find you do not need the aperture, and they're all really sharp at F8 (not that you want to count pores on a portrait!).
Canon 24-70 F4L IS - It's a 24-70, but only 600g, so you save 25% more weight, while keeping the same focal lengths, and you gain stabilization. Pretty sweet. You could trade it out and pocket a lot of cash too as these go cheap as kit lenses. Worth considering.