What is good starting point for timing curve on heavy 4X4?

My F250 4X4 weighs 5200 to 5400 pounds.
It has mild-build 466 cid (TFS alum heads, MSD 6AL ignition and MSD distributor w/ported vacuum advance, 870 cfm Holley w/vac sec., 1-3/4" hedman headers, compression about 9.5:1, cam will be 209/216* @.050 with .552" valve lift).
It has 9" inches of lift (suspension and body). The tires are 37" OD and gearing is 4.56.

Out of the box (the MSD P/n 8477 distributor) is using heaviest springs and max advance is 21*. Advance curve/rate is slowest and maxes at 4,000 rpm. I have base timing at 12* BTDC.

How fast should advance rate be (on this heavy truck) and at what rpm should all the advance be in at?

Thanks!

Edit: 99% street driven, no towing.

Maybe this is the wrong place to ask about street-legal truck. Seems like most over here are running strickly off-road trucks.
But - in case anyone is interested,
On another forum, it was recommened to set advance curve to have all mechanical advance in by 3,000 rpm and set base at 14 BTDC, and limit mech to max of 21 deg (i.e. 35 total).

You are correct that most of the engines we deal with are more high performance style engines, but I'm still surprised that nobody has replied to this.