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It's nowhere close to twice as fast, and in certain use cases can actually be slower, and many system extensions and third-party programs will either not work or may have issues, so it's not recommended for just about anyone. I think the fact it's not enabled by default, and in fact requires a bit of research and a bit of a hack to even run in the 64-bit kernel by default should be a tip-off that it's probably not for the average user.

In other words, you're not likely to see much (if any) benefit, and it's very possible it could cause issues for you, so don't try unless you find that exciting. I personally prefer my machine to work, so I run the 32-bit kernel for now.

jW
 
If you have large amounts of ram (8gb+) it can help significantly with addressing issues
 
If you have large amounts of ram (8gb+) it can help significantly with addressing issues

I think the OP was talking about the Kernel running in 64 bits. The apps are 64 bits fine anyway, even on 32 bits Kernel.

I have my Mac Pro on 64 bits Kernel for months now, and haven't had any issues. Only when SL was just available, did I have an issue with either Fusion or Parallels.
But, other 3rd part kexts can go wrong of course.
 
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