As expert for pre-code horror I can tell you that 7 pages were the norm.
Some companies packed even shorter stories (mostly Atlas) and presented 3-4 page "quickies" (as I like to call them).
They are in general quite bullshitty.
Please try the horror books from ACE (Beyond, Web Of Mystery, Hand Of Fate, Baffling Mysteries) - though 7 pages as well, they are quite elaborate and "wordy".
Get a whiff of them here:
http://aces-of-ace.de/And another tip:
Fawcett horror books feature three long 10-page stories (up to the beginning of 1953).
Go look for This Magazine Is Haunted, Worlds Of Fear and Beware! Terror Tales.