How to test a kernel without messing your system:
Name the kernel you want to test "mach_kernel(dot)something", e.g.: mach_kernel.anv
Place it on the root of your system and reboot. Go to boot prompt and type the name of the kernel you want to boot with. Any problems just reboot normally. This works with any Bootloader i know!
Another tip: you can try create a "rescue" disc with your patches in it, to boot your system from it.
Use INSTAHackintosh, Slimbuild or any of the pre-boot CD's guides around (munky's thread, etc...).
You can easily boot your messed up system with "rd=diskXsY" or UUID at boot prompt.
Note that this may not work in case of "extreme mess"
Till today never failed for me! using mainly INSTAHackintosh but, tested pre-boot CD with success.
LiveDVD is another option
Some more info about the kernel:
-XBench doesn't show me any difference between using this kernel and Voodoo! though, i noticed some faster loading times for some apps.
-You can specify Mac model in Boot.plist under "kernel flags", e.g.: macmodel=MacPro3,1
-It has Decrypter built in so, you don't need decrypter kext. Voodoo team doesn't do this because of legal issues!
I tryed to warn you guys about the installer but, i guess those of you who had problems with it, either didn't read my post (didn't catch the tip??) or the thread i suggested
use only the kernel and update any 10.5.5 kexts you have (system/seatbelt) to 10.5.6.