The signs that my clutch were going were exactly the second test, in higher gears just put your foot down and see how the revs react, if it revs up then returns to a lower rev count before pulling then you have a car that is starting to slip on the clutch.
Also, when my clutch went I noticed the biting point was very high, I know its not indicative of a clutch going but if you have some slippage and the clutch is high there is a fairly high chance its on its way out. Usually the dealer cost of repairing a clutch is enough in itself to convince someone to sell up!