It's a confusing to read because the ifdef structure was changed, but I think the net effect of the patch was indeed to change x64 from 2mb to 8mb (and x86 from 2mb to 1.5mb).
Bug 1537609 Comment 18 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
~~n/m you got it (and I can't delete a comment)~~