I've read most of the condensing boiler discussions in this group and as a
result decided to fit a standard boiler - mainly because of not being able
to upgrade old radiators to work with the lower return temperature.

I was helping a friend select a new boiler and told them the same story but
then realised I might be missing something.
They have a heated swimming pool via a heat exchanger plumbed to the CH.

What if they put the heat exchanger on the return flow?
That would drop the return temperature even if the old radiators didn't.
Am I being too simple minded?
mikej