I agree that 4 pages is a good size, especially after finding out there is enough room to fit 2,600 words. Others have managed more.
I suspect there are a lot of people would struggle with only 4 pages to write a gamebook in. I've also found in the past adventures I have written have ended up anticlimactic and that problem is so much easier to fix when you can just write more bits, rather than working out how to revise or rewrite what is already there.