Super Yamato

Assume base speed = 25, then speed cap = 25 * 1.7 = 42

Total Engy Ability needed for number of engies vs speed
speed engy2 engy3 engy4 engy5 engy6
38knots 6.61 mm 8.10 mm 9.35 mm 10.46mm 11.45mm
39knots 7.63 mm 9.35 mm 10.79mm 12.07mm 13.22mm
40knots 8.65 mm 10.59mm 12.23mm 13.68mm 14.98mm
41knots 9.67 mm 11.84mm 13.67mm 15.29mm 16.75mm
42knots 10.69mm 13.09mm 15.11mm 16.90mm 18.51mm

And given the table of Total Engy Ability, here is the overheat time you would have:
# of engies engy2 engy3 engy4 engy5 engy6
38 60secs 74secs 85secs 95secs 104secs
39 69secs 85secs 98secs 110secs 120secs
40 79secs 96secs 111secs 124secs 136secs
41 88secs 108secs 124secs 139secs 152secs
42 97secs 119secs 137secs 154secs 168secs

Yamato:
This assumes the base speed is 24. Speed cap = 40 = (24 * 1.7)

Here is a table by number of Engies of True
Ability required for each OH speed.

engy2 engy3 engy4 engy5 engy6
36 4,322,190 5,293,580 6,112,500 6,833,983 7,486,253
37 5,382,850 6,592,618 7,612,500 8,511,034 9,323,370
38 6,443,511 7,891,656 9,112,500 10,188,085 11,160,488
39 7,504,171 9,190,695 10,612,500 11,865,136 12,997,605
40 8,564,831 10,489,733 12,112,500 13,542,187 14,834,722

If you have the True Engy Ability shown above you will receive this much OH
Time (in seconds).

engy2 engy3 engy4 engy5 engy6
39 48 56 62 68
49 60 69 77 85
59 72 83 93 101
68 84 96 108 118
78 95 110 123 135