Theoretically it's better to maximize leverage, however there ar

1 is the transaction cost, 2 is the utility of cash

 

if you want to cash out when it grow to a factor a, and the cash out down ration is b, and the new purchase finance down ratio is c (usually b != c), and assume the transaction cost plus lost of utility add up to be a factor of m, then it is better to cash out when:

a((1-b-m)(1-c)-c(1-b))>(1-b-m)(1-c).

Say if b=c=25%, m=10%, then the cash out point is approximately 150%.