Incline is always set at 1%, but speed varies, dunnit. Depends on form and how I'm feeling. Currently I'm struggling to get through 5k at 6.5 mph, I guess due to the lack of carbs - or it could be psychological, I suppose.
Under normal circumstances I use 7.2 mph which is a 26 minute 5k. Any faster than that and I start to ping hamstrings or suffer with gnee.
Yes, I'm at 6.6mph, which basically means 5k is done and dusted inside half an hour. Changing the incline sounds like a good idea in theory, but when you're doing it, it's really the last thing you want. G uses it quite a lot for her girly walking workouts, though.
My only - very minor - criticism of the machine is that its speakers are a bit pathetic, which means that unless you're listening to music, you can't make out your audiobook or podcast over the noise of the treadmill and the fan. I've gone back to using earphones, tbh.
I spent ages pushing to go faster and faster and just kept damaging myself, so it was completely counter-productive. I may even decide to stick at around 30 minutes in future. Better to be able to go 5 times a week than push so hard you're needing more rest days.
I've never used the inbuilt speakers - I jury-rigged an old amplifier and speakers with a cheap bluetooth connection so I can blast music as loudly as I like. The inbuilt fan is a bit silly, though.
I can never manage to concentrate on a book or podcast while I'm running. i just feed off loud guitars.