well if he is using the older version of Nvinject it won't work on anything above 10.5.3(if I recall) there was an issue with the code but they did release a new one to fix this
but it isn't personal preference It is just NVkush fixes this problem
But it is best to use an efi string as you don't have to worry about kexts not working with updates and what not

what is your card axhi
i know it is 8600 GT but how many MB