I find very stupid that XP64 has a 2GB/3GB limit for 32 bits applications. Old 32 bit applications never can request more than 4 GB, but 4GB is larger than 2 or 3 GB it would be no problem of allowing 4GB.
Newly written 32 bit application are able to request more than 4GB using the new RAX, RBX, etc registers even if are runing in 32 bit mode, so why the reason for a 3GB limit?
It looks as XP64 is like Windows 3.1 that was supposed to be 32 bit and really only was 16 bits with some 32 bits addons.

Stupidity also evolves!