For the stack, I'd want it to be the nearly the same, to 10mm taller. I wouldn't want a stack that is more than a couple mm lower.

For the reach, I'd want it to be no more than 5mm longer. Up to around 7mm shorter would be fine (difference can be made up with a slightly longer stem). That shorter margin in the reach may find you with the front wheel closer to your toes (check the front-to-centre distance if listed in the geo chart).