Actually this notion that Sampras was winning all their grand slam matches on fast hard courts, while Agassi was winning all their slam matches on slower hard courts is a bit of a myth.
The conditions at Melbourne in 2000 were playing unusually fast that year, and many players, including Sampras himself were actually complaining that they were too fast. In their semi-final, Sampras served 37 aces, the highest number he served in any match during his career.
That match definitely wasn't on a slow hard court.
It was pretty well documented that the courts at the US Open were pretty mid-paced in the 90s until they were sped up in 1997, before they slowed down again after 2000, and Sampras and Agassi never played each other on the 'faster' hard courts at Flushing Meadows from 1997-2000. Thus the US Open courts that Sampras was beating Agassi weren't exactly overly fast.
Many players were complaining about the US Open courts being too slow for their liking in the early 90s, and there were strong suspicions that the USTA had slowed them down to help their cash cow and one star Agassi (casual fans in the US couldn't care less about Sampras).
Thus the Australian Open surface that Agassi beat Sampras on in 2000, was faster than the US Open surface that Sampras beat Agassi on in 1995, 2000 and 2001.
And really when you are talking about two of the greatest hard court players of all time, slight differences in the conditions of the hard courts don't matter that much.