Clapotis to the Rescue

For months, I have been sitting on the perfect yarn substitute for Clapotis, without even realizing it! The scarf in the pattern is made with Lorna's Laces Lion and Lamb, which is 50% silk and 50% wool, and $30/skein. For 300 600 yards, that's $90.

I, however, have this hand-dyed beauty from School Products, which is 60% silk and 40% cashmere, and for which I paid $27 for 270 yards. It's also worsted weight. Truthfully, I didn't know I wanted to knit a Clapotis until now, but still, it's remarkable. You see, I bought this yarn about eight months ago, in deviation from my usual habit of having a pattern for each yarn purchase, because I loved it so (despite me being torn at the nauseating patriotism of the whole affair, red / blue, you see...). These were the last two skeins in this colourway. I had no idea what I'd do with two skeins. Clapotis to the rescue!

Does anyone know how wide a scarf 270 yards will get me? Should I alter the pattern to narrow it? If so, how much? How many yards does the full scarf actually take?

NOTE: Thank you, Lauren, for helping me out here. I need a lot of help. It looks like once again, I can't read or do math. The SP 60/40 hand dyed is still cheaper than the LL, at $54 for 540 yards (a bit less than the full-size Clapotis) versus $90+s/h for the LL. But sigh, I don't have enough of it to make a full, or even really a 1/2 sized Clapotis... do I?