A researcher fits a simple linear regression model $Y = \beta_0 + \beta_1 X + \epsilon$ to $n = 20$ data points. Given that the total sum of squares $SST = 500$, the sum of squared errors $SSE = 125$, and the sum of squares of the independent variable $\sum (X_i - \bar{X})^2 = 80$, what is the variance of the OLS slope estimator $Var(\hat{\beta}_1)$?