Another rule of thumb: Cut down the examples to the minimum necessary to cover what's being tested.

It makes it easier to read the examples, and it also keeps developers from hacking on to random records for random reasons.  This test checks record 247.  If another dev wants to check another situation, maybe they'll attach to record 147?  Or 42?  Or they'll test for random strings ("Rice", "Imelda").  Or they'll change the value on a random record to test for a specific thing, but not know that another test just happens to be testing for it (like if I changed "Rice" to nil for a nil check).  

Or worse, a developer will create new fixture files for very precise tests, which another dev might tack onto for another random reason... in general, testing off of big fixtures can turn into a mess quickly.