Reading the GCSE/IGCSE debate with interest. I have had DD1 at state doing all ordinary gcses, while DD2 has switched at year 10 between the two systems and does a mix of gcses and igcses.
She finds most of it easier at new school(and coursework helps in her case for history and english). English they don't have to do shakespeare which totally shocked me!
However, she has been working with my mother in law a bit on the maths, where she was in set 1 in both systems.
Mother in law, who was head of maths in a good state and worked with DD1 too, says IGCSE is 'not harder but different'. Less word problems, more pure maths, more marks loaded on the harder questions at the end. There is no non-calculator paper in IGCSE, so she isn't picking up marks for finding mental maths relatively easy.
Horses for courses I guess on that one. DD2 finds the final questions very hard indeed - which she didn't on the GCSE. But that may just be because her particular weakness is spatial and she really really hates 3d trig.
Proof will be when she gets the actual results though.