OK, it is some time since I posted in this thread. 5 months on I still do not have a confirmed diagnosis. However I have been able to get my GP to prescribe Mestinon on a trial basis. The effect is dramatic.

But this thread is Mestinon vs Caffeine. Whilst these are subjective, and personal results I can know give some answers.

200mg caffeine tablet, claimed to be equivalent to 1 large strong cup of coffee.
CI effect is about the same as 5mg Mestinon.

I am now on 30mg Mestinon every 4 hours. To reach that level of effect with caffeine alone I would have been taking more than the reccommended daily dose, every 4 hours. Clearly that would have caused serious side effects.

But at least we now know... 200mg caffeine is approx equivalent in CI effect to 5mg Mestinon.