I use WGT caddy and the percentages don't help me, however, it gave my a chance to be a math geek.
This is what I came up with:
Slow greens Distance +/- incline x 1.2 = strength needed
Standard greens Distance +/- incline x 1 = strength needed
Fast greens Distance +/- incline x 0.9 = strength needed
Very fast greens Distance +/- incline x 0.84 = strength needed
Tournament greens Distance +/- incline x 0.77 = strength needed
Legend greens Distance +/- incline x 0.72 = strength needed
Championship greens Distance +/- incline x 0.67 = strength needed
Round up and you should be ok.