How can I tell which version of Voodoo to install?
The difference in the filenames reflects the codename for the kernel version.  The phone only shows the version number, making things difficult.

The good news is that you can use any 2.2 kernel with a 2.2 ROM (or 2.3 with 2.3, etc.).  I'd just use the newest (they're alphabetical, so JS8 is the newest).  You can always experiment and see which one gives you the best performance, or hit up the XDA forums where people will certainly have discussed it.