I had the same question today and I'll report back in a couple of months with my results. I just grew a 240 billion cell starter of WLP001 for an IPA with an estimated post boil gravity of 1.065. This is only my second all grain batch, so I'm not totally dialed in yet and I ended up at around 63% efficiency with a 1.055 post boil according to my hydrometer. Am I going to over pitch? Probably. Am I worried? Not really, because it was an awesome late summer brew session in the northeast. Cheers!