The other answers have given you approaches to estimating the overall rate constant as a function of temperature, which in turn requires you get an estimate of the prefactor, $A$. Knowing rate as a function of temperature is of course useful.
However (and I write my answer not just for you, but for others who might be searching for this topic), your question wasn't about estimating the overall rate; rather it was about estimating the temperature at which the activation barrier could be 'reasonably' overcome by thermal energy: "When are transition state's energy barrier “reasonable” at a certain temperature?"
In response, let me offer a very simple general guideline commonly used by chemists and physicists. The activation barrier is comparable in height to the amount of available thermal energy when:
$$RT \approx E_a$$
I.e., when:
$$T\approx E_a/R$$
At this temperature, the exponential term in the Arrhenius rate expression is simply $e^{(-E_a/RT)}=e^{-1} \approx 0.37 $.
A good number to memorize is that, at room temperature (298 K), $RT\approx 2.5\,\, \text{kJ/mol.}$ This tells you that the average thermal energy at room temperature is within the range needed to break water-water or water-protein hydrogen bonds. It also says you're in the regime where changes in temperature have a significant effect on the stabilty of these bonds. [The stability of stronger (e.g., covalent) bonds isn't significantly affected by temperature changes around room temp, and weaker associations (those due to van der Walls forces) are thoroughly disrupted at much lower temperatures.]
[This isn't to say VDW forces are unimportant at room temp — they are! Rather, it's saying these bonds are in a continuous state of dissociation and re-association at room temp.]