It improves performance of the final conversion step after export. Convenient, but not important as it doesn't change any functionality. The older ImageMagick 6.9 version should have all the files.

Yea, that's it. Portable should be fine. Depending on which ImageMagick version you get (dynamically linked, statically linked, etc, etc,..), there may be some .dll files in the archive, just throw all .dll's in there with convert.exe to be on the safe side. Leave the existing ImageMagick folder as it is.