If you don't need your savings to sustain you, wouldn't you only need your spending 50k x 16 years?
So you need 800K to last your 16 years if you withdraw 50K/year. Again you will draw down the savings to zero so the 4% rule or SWD doesn't apply.
Or you could account for 7% growth each year even when you withdraw 50k/year. Then you would only need ~475K
Year Base Stache withdraw base stache@7% Year end stache
1 $475,000.00 50000 $33,250.00 $458,250.00
2 $458,250.00 50000 $32,077.50 $440,327.50
3 $440,327.50 50000 $30,822.93 $421,150.43
4 $421,150.43 50000 $29,480.53 $400,630.95
5 $400,630.95 50000 $28,044.17 $378,675.12
6 $378,675.12 50000 $26,507.26 $355,182.38
7 $355,182.38 50000 $24,862.77 $330,045.15
8 $330,045.15 50000 $23,103.16 $303,148.31
9 $303,148.31 50000 $21,220.38 $274,368.69
10 $274,368.69 50000 $19,205.81 $243,574.50
11 $243,574.50 50000 $17,050.21 $210,624.71
12 $210,624.71 50000 $14,743.73 $175,368.44
13 $175,368.44 50000 $12,275.79 $137,644.23
14 $137,644.23 50000 $9,635.10 $97,279.33
15 $97,279.33 50000 $6,809.55 $54,088.88
16 $54,088.88 50000 $3,786.22 $7,875.10