Yea, at some point you really can't tell if function 1 grows faster than function 2. Anyway to pick a large m(x).
m(0) = 1; m(x) is the recursion of all finite functions defined using k(m(x-1)) symbols that produce larger numbers than their input defined at stage m(x-1).
So a 1 step function F1(x) = X + X and F2(x) = X ^ X,... including any function that has been included in a mathematical paper to this point that takes one ore more finite numbers as an input.
And because these are all finite functions call them recursively in whatever order produces the largest output starting with the initial input (x). Now, to size this depends on what initial notations are allowed, so m(1) is a finite number.
Next level could then include F#(x) where F1(F2(x)) etc.
PS: The above is roughly equivalent to saying infinity +1 and is not interesting IMO. I can also drop the k from the above, but again the point is to use the dumbest approach that works.