Connecting spending to tax cuts and GDP growth

These numbers are always being thrown around, but where are the primary source reference?

70% of US GDP is driven by consumer spending. (source? probably BEA)

Average consumer unit:
Age: 49
Number of persons in consumer unit: 2.5
Income before taxes: $62,857
(source: US Dept Labor, US Bureau of Labor Statistics, 2010)

Average annual expenditure: $49,067
(source: US Dept Labor, US Bureau of Labor Statistics, 2010)

So...

If you believe the hypothesis that tax cuts effect consumer spending, which subsequently increases GDP growth, then for tax cuts to be most effective, they should targeted the average consumer unit.

Since the average consumer makes considerably less than $200,000 annually, any tax cuts should target the tax brackets around $65,000 annual income.

Some assumptions:
1. The average consumer unit represents most of the 70% of consumer spending of the GDP.
2. Consumers will be more likely to boost spending if the change in tax liabilities is permanent.
3. Consumers will wait to increase spending until a tax change affects their take-home pay.
(source: "The effect of tax changes on consumer spending"Steindel, C. (2001) Current Issues in Economics and Finance)