You are fine removing natit.kext. As pointed out above, that is only needed for hackintosh.
So what exactly does removing vs not removing that file do if you have the official Apple 4870? Would it in any way result in decreased performance if it's removed and you have the official card?
Also, there shouldn't be any need to somehow uninstall or remove the overall installed drivers once 10.5.7 is released, right? It should all update properly with what I assume are different/improved drivers, at least for non-2009 mac pros? Thanks!