I was sceptical a couple days ago when we briefly discussed this, but I've since staked (twice!) with ~1.2-1.5k GRC. So we learn:

• The staking rate has a large random component
• One appears to be able to stake with ~1k GRC in a semi-reliable fashion within the six month window that @dutch was concerned about in his excellent post on the topic of staking rates.
  I'm trying to think up a way to survey staking rates for people with wallets in the, say, 500-3k GRC range since V8 came out.