how would that affect the bike , more control and stable at speed , or less stable at speed but better at slow speed ? thanks

More aggressive and direct steering perhaps, though the stem length isn’t massive.

Not sure how much it would affect straight line stability but given you have more leverage, it should in theory feel more stable in rough terrain. I don’t think it’ll be a revelation or owt.

Chances are you’ll be used to it in ten minutes.

Watch out for trees.

The shorter stem will make it slightly more twitchy at speed, and along with the wider bars, a little bit more agile at low speed, e.g. on techie climbs.

You’ll hardly notice much difference though – it’s a small change.

Probably trees will feel the difference more than you.

Descents might feel a bit more relaxed, climbs may be a bit less efficient.

That was observation anyway.

You will find you will start to clip walls, trees, etc and knock things over when you pull the bike out of the garage.

I found 750 was my sweet spot