According to BT my line is suitable for Infinity 2, which is what I have. However my current speed according to speedtest.net is around 25 Mbps down and 6 Mbps up. Would these values stay around the same on Infinity 1?
Yes, there will be absolutely no difference by changing to Infinity2. Infinity 1 is just an artificial cap on speed so if you are below the cap nothing will change. What does https://www.dslchecker.bt.com/ show your line capable of?
... and if he continues to use the same set up he used to produce the above results on Infinity 2 it will still show the speeds he is getting now
I think my eyes are painted on this morning! I read it incorrectly that the OP was wanting to upgrade from Infinty 1 to Infinity 2 not the other way round.
thanks, it shows my line is capable of 50.6Mbps high or 37.9 impacted, but I never see those speeds. On a direct line to my router at quiet times the highest I can remember was 35
Definitely downgrade, even if you could get 50M the difference to 40M would be negligible.