Which Saddle?

It should give you another few mm. It might be easier and cheaper to insert a layback post the other way around.

Okay, so we are not talking centimetres here.

^Yep, Gastoning it is probably a good idea, it'll give you a greater safety margin until you buy a smaller bike.

Pythagoras, I would have this issue on any sized bike that has not a 74° seat tube.