So I can confirm that the 300 actually does work for straining out break material.
I brewed yesterday and unfortunately was on auto-pilot at the time of the first hop addition. I dumped them right in and forgot all about the strainer sitting in the bucket of sanitizer next to me. So, crap, but I figured if I wasn't blocking them during the boil, I'd try to strain them out at the end.
So, after I cooled my wort and let it sit for awhile, I gently lowered the strainer into the pot, put my siphon inside it, and took out a few gallons of crystal clear wort.
As I got to the bottom of the pot, this stopped working, because the screen was pretty much clogged and wouldn't allow clear wort in as quickly as the siphon was taking it out. So I removed the strainer, hosed it off, re-sanitized it, and then hung it on the side of my fermentation bucket. Then I just poured in what was left in the BK. There were probably two quarts worth of wort, hops and break material left at this point. It didn't drain quickly, but I got another quart of good wort out of it, leaving at the end this: