If you go in to your user profile you can change the viewing options in your profile. It then takes effect across the forums. It is not a server side option, it is by user option in each users account.
Go to: My Account - Edit Options - (then modify these three choices to your desire)--they are near the bottom:
Thread Display Mode - choose linear, oldest first to be like the old forums
Number of Posts to Show Per Page - 25 for the old forums settings (your choice though)
Default Thread Age Cut Off - Show all thread to be like the old forums (your choice though)
As an FYI, mine are 'choose linear first', 30 posts per page, and show all threads. But that is just me, other will have other choices.
I also use the standard editor, not the enhanced editor. The enhanced editor seems to have a few problems with vbulletin. We will fix them up I am sure but I would suggest you use the standard editor.