According to our Proposal Guidelines, it is still acceptable as it says:
There was some debate some time ago about lowering the limit to 300 pages, but the outcome was that
(Of course we can reevaluate that outcome any time 
I personally am not that pessimistic when it comes to limiting proposal lengths to 300 pages.)
Bumping up the reading right from the start feels to me like breaking the “speed promise” to those who voted and who are interested but might have a harder time keeping up with the reading speed. But that doesn’t mean we need to be tied to a fixed schedule throughout the whole book. Therefore my suggestion would be to start out with a standard 15-ish-page schedule and to vote on increasing the speed after 4 weeks or so. This way, we have a much better grip on how difficult the book actually is, and the participants have a better grip on how well they can manage reading the book, so they have much more information on which they can base their vote.
If possible, I would like to defer the details of that discussion to the book’s home thread 
Naphthalene, if you’d like to run the book club, would you mind setting up a home thread for it so we can continue the book-related scheduling discussion there?