Spacing of 6x6 would grow the trees very tall and straight; however, you would have little screening as most lower branches would die off due to the crowding. I plant 9' apart. You then space the rows 18' wide (hazel, dogwood, etc.) and plant shrubs between the rows.
Norway Spruce is a much faster grower.
Some notes I have developed on both trees:
WHITE SPRUCE Moist/Shade Tolerant
(Picea glauc) 75' Zone 3. It has a silver-green foliage on pendulous branches. Tolerant of wind, wet soils. White spruce is tolerant of a considerable amount of shade and does not like high heat of the summer. Moderate growth rate and it’s best growth is on moist, acidic, loamy soils and is often found on stream banks, lake shores and adjacent slopes. The needles are single, four-sided and crowded along the branches. They are 1/2 to 3/4 inches long; sharply pointed; and dark bluish green when mature. The cone is 1 to 2 inches long, cylindrical, thin and flexible when mature. The cone scales are rounded and soft at the ends. The white spruce grows to about 60 feet tall. It is densely foliated and has a straight trunk. The bark is dark gray or gray-brown in color. Its foliage and twigs are eaten by white-tailed deer. The tree provides cover for many species of wildlife.
NORWAY SPRUCE Moist/Partial Shade
(Picea abies) 100-150' Zone 2. Very fast growth. Valued most for windbreaks in cold areas and timber production. Extremely hardy and wind resistant. A native of Europe, the Norway spruce has been planted widely in this country and Iowa for ornamental use and for windbreak plantings. It is a large, fast-growing tree requiring a fertile, moist soil. The needles are single, angular or four-sided, yellow-green in color, 1/2 to 1 inch long and slightly curved. More of the needles are borne on the upper surface of the twigs where they usually point forward. The foliage appears to droop or weep. The cone is 4 to 7 inches long; light brown; hanging down. Norway spruce grow 75 to 100 feet tall. They make good winter cover for wildlife.