I am using a 12 page writ of cert to the state supreme court I wrote over the course of this summer job. I debated just sending the argument section (its fairly short as the argument was not very complex) but decided to just send the whole thing. I figure if they truly only want to read a few pages, they can skim it or only read portions. I think the key is to send a QUALITY writing sample, regardless of length or subject matter. Perhaps if they have 5-10 pages underlined, in bold and with an exclamation mark after it, I'd only send that many, but I figure most employers are flexible.