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It would be pointless for an existing 4.6is owner to trade up to a 4.8is.
It seems like this thread will take a biased approach. All the 4.6is drivers will say it's probably not worth it, while the 4.8is drivers will say go for it. It's really about what you want and how much of a dent you want to put in your wallet. The 15 HP difference just wouldn't be enough for me. Now some might argue that going with either one over a 4.4i is not worth it. Again it's about what you want..........Phil