/PAE doesn't change the user and kernel virtual address space assignments that were changed by using /3GB, but, you should not use /3GB and /PAE at the same time. Per Microsoft:
When the physical RAM in the system exceeds 16 GB and the /3GB switch
is used, the operating system will ignore the additional RAM until the
/3GB switch is removed. This is because of the increased size of the
kernel required to support more Page Table Entries.
You need as much kernel memory space as possible (more than 1GB) just for the page table entries to describe more than 16GB of memory.
Edit: Also per Microsoft:
The conflict is when we use the /3GB with /PAE simultaneously. When we
are using PAE the OS needs to manage lot of resources which needs more
memory than 1 GB. So certain operations have performance issue and
then fail intermittently.