I have viewed footage of tilden, but i dont find him particularly athletic or nimble, flexible compared to the athletes of today. He seems a bit gangly and not as fast as say for example borg or laver on the court, or as agile/fluid as federer. But that is besides the point. Comparig either fed/samp to tilden is very difficult because the structure of global tennis landscape has changed significantly over many generations between these players. Also the technology, and the surfaces are different. Comparin federer to sampras, however is not as difficult because you are really only talking about at most one generation in between the two players, if you can call it that. Much of the criteria used to compare federer to sampras is quite valid given the fact that the structure of the ATP and ITF hasnt changed too much. Therefore using numbers to compare leaves less room for interpretation because the variables havent changed as much between federer to sampras...as say federer/sampras to tilden.