relationship between block size and detected frequencies in goertzel algorithm
Since Görtzel computes a part of the DFT, the relation between detectable frequencies is the same. So with 8000Hz sampling rate and 600 samples you cover the frequency range of -4000Hz to 4000Hz with 600 frequency intervals, and both your frequencies are points of the subdivision, thus both should be perfectly detectable. 

Can you show the code for the Görtzel iterations?



Or even before that, did you build the test signals using $\sin(\pi\cdot f\cdot t)$ or $\sin(2\pi\cdot f\cdot t)$? Only the second gives the correct frequency, the first could explain your observations, since the 600 samples would then contain $12.5$ periods of the oscillation for $f=333.33Hz$, but full $5$ for $133.33Hz$.