Consider for positive real $x$ :
$$ f(x) = \sqrt x^{{\sqrt[3]{x}}^{\sqrt[4]{x},\cdots}} $$
How does this function behave ?
How fast does it grow ? Faster than any fixed iteration of exp sure, but How fast exactly ??
A brute estimate would be $\operatorname{tet}( \ln(x+1))$ but that would likely be a bad estimate. We have to do better.
update
$f(2) = 1,54752264961525$
With Mathematica there is a loglog plot
$$\text{ListPlot}\left[\text{Table}\left[\left\{x,(\log (\text{$\#$1}+1\&)\left((\log (\text{$\#$1}+1)\&)\left(\text{Fold}\left[\text{$\#$1}^{x^{\frac{1}{\text{$\#$2}}}}\&,x,\text{Range}[2,10000]\right]\right)\right)\right\},\{x,0.1,1.5,0.01\}\right]\right]$$