No, there are no official portable zipped distributions, but you can make one yourself, it's quite simple. Here's an instruction on how to do it for JDK 7 (for JDK 8 the procedure should not be different):

http://www.brucalipto.org/java/how-to-create-a-portable-jdk-1-dot-7-on-windows/

In a nutshell, you should unpack the .exe file as a 7-zip archive and rename all of the *.pack.jar files inside to corresponding *.jar files (just remove ".pack" from their names).

64-bit vs. 32-bit really boils down to the size of object references, not the size of numbers.

In 32-bit mode, references are four bytes, allowing the JVM to uniquely address 2^32 bytes of memory. This is the reason 32-bit JVMs are limited to a maximum heap size of 4GB (in reality, the limit is smaller due to other JVM and OS overhead, and differs depending on the OS).

In 64-bit mode, references are (surprise) eight bytes, allowing the JVM to uniquely address 2^64 bytes of memory, which should be enough for anybody. JVM heap sizes (specified with -Xmx) in 64-bit mode can be huge.

But 64-bit mode comes with a cost: references are double the size, increasing memory consumption. This is why Oracle introduced "Compressed oops". With compressed oops enabled (which I believe is now the default), object references are shrunk to four bytes, with the caveat that the heap is limited to four billion objects (and 32GB Xmx). Compressed oops are not free: there is a small computational cost to achieve this big reduction in memory consumption.

As a personal preference, I always run the 64-bit JVM at home. The CPU is x64 capable, the OS is too, so I like the JVM to run in 64-bit mode as well.

Don't rely on the java.exe that's in a Windows system directory; add the bin directory of your Java runtime environment to the PATH environment variable (if that's not too much "messing around with the system configuration").