With the 4v you're looking at an easy 6500rpm useful limit and you'll want every inch of it (you can go to 8K easy but since that's not for you... 6500 is fine). That's a good stopping point anyway. Piston speeds get kinda high on the 5.4 after 6500. FWIW, 7500rpm on a 4.6 produces the same piston speed as a 6500rpm 5.4. With those free flowing heads you're looking at nice returns without having to spin crazy rpm because you have crazy long stroke.
You'll want a non-stock cam grind no matter what to make proper use of the cubes. A set of 4v cams is a grand retail. Add another grand for springs and locks, seals, etc... A set of FR500 cams would be about killer for OEM stuff and can usually be found used.
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