I live at the bottom of Florida so cars sell for slightly more here given that a Florida car has never been subjected to cold temps, snow. ice, , road salt, huge potholes, etc.
I think $6,000 is approaching the high side for that many miles. BUT ... the person who buys your car will get something most buyers won't get: a car that is up to date on all maintenance, a young engine replaced by someone who did it properly, and a V8 that has not been tortured at the track, and top tech features rare in 2006 cars. Plus, it has bourbon leather (rare) and the rear seat theater system with surround sound. You didn't mention it, but it appears to be accident free, and has a clear title (no flood, salvage, etc). There is an 06 M45 with 142k miles, no NAV, and it is at a dealer for $5,950 - will likely sell for less. Yours is better equipped, has lower engine miles, and the bourbon interior/black exterior which most people find most attractive.
I would price it exactly where you did, and possibly let it go at about $5,500.