How high is "high impedance" on this chip (CD74HC125E)
Here is a direct link to a datasheet, since "alldatasheet.com" has gone offline.

If you look at the top of page 4, the parameter you're looking for is IOZ, output leakage current. It is given as &plusmn;0.5 &micro;A typical at 25&deg;C, &plusmn;5 &micro;A worst-case over the commercial temperature range. This translates (assuming VCC = 5 V) to resistance values of 10 M&Omega; (typ.) and 1 M&Omega; (min.), respectively.