What is the ideal DD width to use for jp2 and DEM generation?

the assumption here is that tiles are 1024 pixels square at a latitude of 0 (zero) degrees, ie the equator

length of the Degree in lat is 110574.2727 meters

assuming this calculator is accurate

http://www.csgnetwork.com/degreelenllavcalc.html

to get the size of one pixel you would calc the following:

110574.2727m x .0.0016 / 1024 = 0.17277230109375 meter = 6.8 inches

DD

tile w ratio(degree/pixel)
0.0016 0.0000015625
0.0128 0.0000125
0.1024 0.0001
0.8192 0.0008
6.5536 0.0064
52.4288 0.0512

METERS tile w ratio (meter/pixel)
250 0.244140625
2000 1.953125
16000 15.625
128000 125

METER - DD
LAYER ; TILE WIDTH DD ; IDEAL PIXEL/UNIT RATIO

layer 1 ; 0.0016 ; 0.0000015625(about 0.142 meters)
layer 2 ; 0.0128 ; 0.0000125(about 1.136 meters)
layer 3 ; 0.1024 ; 0.0001(about 9.1 meters)
layer 4 ; 0.8192 ; 0.0008(72.72 meters)
layer 5 ; 6.5536 ; 0.0064(about 581.81 meters)
layer 6 ; 52.4288; 0.0512(about 4654.54 meters)