So much bs that I don't even want to go further into discussion, sorry. I say this as someone who has made several thousands of espressos on E61 group machine. I'll let you have your own opinion but anyone who has made more than a few espressos will immediately understand if and when the temperature drifted away. Pressure? I've made espressos at 6 bars and 9 bars. Makes literally almost no impact or whatsoever. You're right though that 5 degrees Celsius is probably about the right minimum amount when the espresso starts to change in taste, and there's remarkably many machines which cannot sustain the temperature in shot after shot workloads.