Brad's (generic) rig guide and also the tuning guide for my Sedici both suggest a 'norm' for A Rig hounds position at around 1175mm above deck level.

What would be pros n cons of - for the same (and a 'typical') spreader height - them being 100mm higher...?

In theory you can calculate the best position for the hounds and the spreaders if you know the loading on the mast (assuming you goal is to minimise the mast bend). In practice the loading varies with so many things (incidence, camber, mainsail twist, wind speed, etc.) that I'm not sure it's worth trying. Perhaps it is easier to consider what happens at the extremes and then decide if your rig is tending towards one of them too much.

If the hounds are too low then the top of the mast will bend off too much, the leech will open and you will likely get a crease running down from the hounds towards the clew.

If the hounds are too high the mast may bend excessively between the hounds and the foot. This may well induce a crease form the hounds to the clew. It will definitely stiffen up the top of the mast and lessen the tendency for the leech to open in a gust. Is this a good thing at the top end of the rig's range?

I think the spreaders should be at a point where the bending moment above them is equal to the bending moment below them i.e. at the height of the aerodynamic centre. But of course the aerodynamic centre moves around with the same variables (particularly mainsail twist).

Personally I would go with practical experience and perceived wisdom unless I was trying to cure a particular problem with the rig.