Hard to tell but looks to be about that of Blackarrow's chip, so we know that they could get at least 100W out of it. But yeah smaller than I expected.
Not that hard to tell - the chip silicon and substrate sizes are in the datasheet after all. SF3301 substrate is 19x19mm. Minion is 25x25mm - a fair bit larger, while KnC's public offerings were a massive 55x55mm.
It should be the same size as Spondoolies-Tech's RockerBox, which you're familiar with.
( A bunch of this data is in the wiki )