Screed Depth for UFH (& Insulation)

UFH provider says 75mm min and 125max for UFH screed on ground floor

Debate is to go to 100mm (better thermal mass of floor so more heat stored but more expensive and a slower reaction time for heat up/down) versus leaving it at 75mm (cheaper but lower thermal mass)

Any suggestions - don't need the extra 25mm for anything structural so its purely a 'which would be better' call. Currently spec'd at 75mm

Also floor insulation underneath is spec'd at 100mm. Should I increase this to 120mm or is it not worth the additional spend (versus return)

Interested in all opinions and experience with UFH screed depths and insulation under? Tx

increase insulation to 125 and pour 75mm reinforced screed.

I have generally heard 75mm is the recommended. That's what I went for.
Also I used 100mm insulation in 2 layers of 50mm. I think it worked out cheaper that 100mm funnily enough. Also I laid top 50mm layer in such a way as to stagger joins, ie. different joins in bottom layer from top layer. Think it worked out a bit more stable this way.

For downstairs I used 100mm of kingspan and 90mm of concrete. For upstairs I used 70mm of insulation and 75mm of concrete.
The greater thermal mass downstairs should keep the heat longer where most of the activity will be during the day.
Upstairs should heat up quickly before everybody gets up and same thing at night.
From talking to people who have UFH everybody I know it takes a while to fine tune the system to your exact requirements its a case of experimenting to see the most efficient heating load