Actually that spread is smaller than I would have expected intuitively. How did you calculate it? Did you base it on the assumption that on average a block is found every x minutes (and then applying a poisson distribution), or did you use crunch the numbers calculating for every GH/s the chance of finding a block ? The result might (should?) be the same, but Im a little hesitant to accept that as fact.

I believe the spread is correct, but this one is based on a Poisson distribution. The calculation is based on a C program I wrote that uses the MPFR library (I couldn't find an online calculator that could handle 2016! without a huge loss of precision :-))

I've been building another simulation and wasn't overly happy with the way I derived some predictions using the table so I've now got this based on running random simulations of mining and using an exponential probability (which should give the same Poisson behaviour but lets me be more precise about the 2016 block chunks).

While I've not run a statistical correlation of both approaches the simulation results are the same both ways.