If you have more than 4GB of RAM, you’ll need 64-bit software to utilize all of it. It may or may not affect video editing speed, depending on the particular operations you’re doing and how much stuff regularly gets loaded into RAM.
If you want REALLY fast video editing, get 16 or 32 GB of RAM and create a RAM disk out of it (but back up often).
Bit-ness has nothing to do with the archives created, although file size might. Older computers might not support RAR files larger than 4 GB, for example. That’s a product of the filesystem (FAT vs NTFS, etc.) and not whether your software is 32 or 64 bit.
In any case, there’s no reason to be making RAR files anymore. They’re proprietary, slow, bloated, and unpopular.
ZIP is fine for 90% of uses and works out-of-the-box with most major operating systems (Windows, OSX, Android, Linux). For purposes where RAR’s better compression is needed, 7-zip is free, open-source, faster, and compresses better. And anybody who knows how to open a RAR file these days will likely be able to open a 7z file as well, and if not, you can always make self-extracting 7z archives. Let RAR die already.
Or if you have a 2nd-generation or later Intel Core i3/i5/i7 CPU, using the onboard graphics processor together with software that supports “Intel Quick Sync” is even faster than CUDA. The difference is still dramatic even with the latest, 4th-generation CPUs and modern GPUs.
In other words: Don’t waste money on a video card if editing is what you want to do. Buy a solid state disk or more RAM for the laptop instead. EDIT: On a laptop, you probably wouldn’t be getting an external video card anyway. But you CAN choose to not use CUDA in favor of Quick Sync, if your CPU and software supports it.