Ikea has the Index rod up to 152"...

I got mine from Smith & Noble who're used by a lot of designers. They need to be heavy duty because that size span puts a lot of stress on the brackets. In fact I ended up using those claws screws after the included screws failed. My curtains were filmy, too. I'd also recommend attaching the curtains with matching rings. Makes the whole transit thing a lot easier.

I would not put up drapes in this room. It is beautiful the way it is.

Silent Gliss has a number of different systems.

http://www.silentgliss.com/go/3UUW63A26M9EUY9DQOIMM6G6XY2V6RDV

electrical conduit can be cut to length, bracketed as you need to, and is very, very reasonable. Add finials of your choice.

go with a wire system instead of a rod. Ikea has some but I'm not sure if they're good enough for that long of a length.

The Ikea wire system doesn't work well for distances that long, it sags. I just tried it!

I've seen people use hospital curtains (doesn't sound nice but ) which I think would look great here.

oops. never mind. i just relooked at the picture and saw the beam.

It looks like light control and privacy aren't issues - so why put up draperies at all???

Could you put up two of the C&B rods and meet them in the middle with two hooks side by side? I was going to suggest Restoration Hardware (I have their cast iron collection), but they only telescope to 126" :(

We did something similar at my friends', instead of shelling out for corner rods, we met two rods at the corner, and it's worked out nicely.

I have no help, but wanted to say that the room looks very nice.

I'm a huge fan of Ikea's Dignitet rods (http://www.ikea.com/us/en/catalog/products/60075295). They're super cheap (15 bucks!!), and their near-invisibility prevents them from looking cheap (I normally hate the look of most curtain rods). Very modern. The wire goes up to 196", and you just cut with pliers or wire cutters to size.

Gorgeous windows! What about a woven solar shade in black so that when it is rolled up against the dark wall you don't see it?

If you still want to do the curtains, consider a drapery store for a custom rod or look for extender bars that go with rod sets you like. For example, the maximum rod length may be 108", but the company sells a companioin extender rod that adds another 4 feet. Add as many as you need with extra brackets to support the length.

we used:
galvanized plumbing pipe and coupling joints. you can get one to fit in the middle, as well. we have medium-weight curtains and the pipe does not sag. i loooove the industrial look it provides, and it was super-cheap. price things out at your hardware store and i think you'll be happy!

We went to the Home Depot and bought 2 lengths of 1" copper pipe and a copper joiner piece and connected them in the middle. It works well and looks very stylish with the nice patina it's developing. To hang the curtains, we just bought some ring clips. We've used them for 15 years so far, with no plans to change them.

Go the the hardware store and cut a piece of 3/8" copper tubing. I did this on all my windows, and at $1 per foot, you can't beat the price. FYI old doorknobs make green finials.

A pole top curtain fits over the rod.

This puts up RED FLAGS for me! Silk and sun DO NOT mix. Are the curtains lined or treated? Even a lining might not suffice, I'm afraid when you put up your new silk curtains up they will degrade and you will be left verrry unhappy :(

I have these installed:
http://www.ikea.com/us/en/catalog/categories/range/10374/13289/

You can use panels or sheers. They come in variable lengths which you cut to fit the space. They have rounded corners for the areas where you want the curtain/panel to go around a corner. And the price is right. And you can mount it above the windows ( I have similar ceilings and windows.) I like these because you can add another layer of curtains/panels just by adding another track to the existing tracks. So in the winter, I can have more layers. Plus you can change out the fabric fairly easily.

Good luck!

Wow, I think those windows would look wonderful with a sliding panel system that would stack up at either end. You can get the system from Silent Gliss.

How 'bout dowels? They're cheap, come in many thicknesses, work with many styles of finials and brackets and can be painted to match your decor.

You can get heavy duty, long curtain rods at Made of Metal. If you get the 1.5" or 2", it won't sag with three brackets. The k683 finial looks modern and the matte stainless finish would look great in your room.