Lot of great posts and comparisions. I vote for 4.6is. I have an '03 Dinan 4.6is. Tons of miles, still drives great and the engine spins up fast and strong.....and then there's the Dinan exhaust note. You pay a premium for a 4.8is. I'd buy a 4.6is, pocket the money for the inevitable repairs, or splurge and install a full Dinan system. You'll love it.