Pages are way to small I think they should be like 100 posts each and also for more convenience they should start in reverse. aka, when you click reply you start with the last page and then go to the beginning

also to keep everyone happy it will not hurt to leave option to view all thread in one page, because those pages are only useful for people who are coming back to check for new posts and they don't need to load previous content which they already seen
Those who want to see everything probably will prefer to see everything in one page rather than getting interrupted at random places.