Tricky one that, Ozplane! I guess it depends on whether you count the 367-80 as the B707 prototype - in which case at 39m length it was still shorter than the 41.5m 707-138 - or the first 707-120 as the prototype, in which case you are right, as it was, at 44m length, indeed longer than the -138.
and Cejkovice:
I think you have a point there concerning the A330! Although I cannot recall now whether the A340-300 flew before or after the -200 - what was prototyping what in this case?
I really must look out that anorak somewhere........