Hello, this is my 1st post to the Pascal Game Development Forum
I do believe that any x64 application benefit from x64-mode due to faster arithmetic operations than in x86-mode. May be the benefit is not that straightforward, and as you already said compiler optimizer has more room to work in, but it seems to be general too. Look, I came across opinions that SQL Server x64 is faster than x86 not only due to amount of memory it could address but arithmetic ops too. I wonder what's going on with performance when x86 app runs in WoW64 mode on Windows x64.
Prime95 is an example of extremely optimized x64 application which has assembly language functions optimized for different processor architectures and separate executable for x86 and x64 modes.
In very near future we could see a quite of programs written in Delphi packaged for Windows x64.