Kezo, I’d love the opportunity to design and install a new system. I put 2 in many years ago. As far as I recall Delta T 50 calls for a flow temp of 75 Deg. You must have much better insulation than this 95 year old house can be made to have. It’s heating was always inadequate, pipes and radiators both too small. I’ve replaced most of the rads but can’t do anything about the pipework…
The reason I mentioned Delta was its importance to when your system was designed/fitted. Prior to 2013 the UK was T60, after that it came in line with the rest of the Europe which used T50. So a Delta T60 radiator with an output of 5000BTU would equate to 3945BTU at Delta 50 (BTU at T60x0.789=T50). Most installers or radiator stores compensate fo this depending on the type of home. Heatpump sytems use a much lower Delta raing of arund T30.
If you have a flow temperature from your boiler of 80c in theory the water inside your radiator would be 70c with an average room temp of 20c. 70-20=delta T50 radiator as a guide. The important bit to remember a 80/60 (flow and return) is way way to high for a A/B rated boiler to condensate and be effiecient “A” rated. Most modern boilers condensate at 55-60c (you can check this in your boiler manual) So a modern A rated boiler will quite happily run on T50 radiators at 60c and heat your home to temperatures of up to 25c. At a flow of 60c my radiators are still really too hot to touch if I left my hand on them, but they may take a couple of mins longer to get hot.
As said in my last comment it is important to know the system Joejo has. It equally important that you radiators are balanced correctly.