Don't mean to shoot you down David, but the cruise control does not apply brakes. As far as I know it is not in the specs. Have you noticed the brake light going on at night when you are going down a hill in cruise? Try that out to see & let us know.
I am very sure that there are no brake lights when the computer applies the brakes. It does not apply the brake lights when the VDC kicks in so I don't see why it would do with the cruise-control.
I have not read about this 'feature' anywhere either, but I do feel it ... I can feel the car using the brakes to slow itself down when on cruise control ... especially going down relatively steep hills. I cought me by surprise first few times I felt it, but I'm very impressed with it.
The funny thing is that i've a Track and I've never expirienced that behaviour in my car.
OK, that has me very much baffled now .... I don't see why your car would be any different from mine.
btw, how steep is the hill in question?
I find that the trip computer reader is a bit higher than the actrual speedo, I would say maybe 3-5km higher.
Mine seems spot on ... I checked it a few times on the 'speed check' readout on the Hume Hwy going out of Melbourne. I checked it at 100 - 110kph and my digital speedo was always eithrr spot on, or within 1kph of the readout.
ps. I don't use the analogue speedo, but the digital one instead. Also it seems to agree with the speeds in gear (at least my one does). ie. bounce the 2nd gear of the rev-limiter (ie. 6,600rpminthe manual) and the speedo will read 98 - 99kph. Same thing in 3rd ... it'll read just over 140kph. Have you got non OME size tyres? That may be putting the reading off.