All hard to say. If we look at Sampras for example, Rosewall would competitive on all fast surfaces with Pete Sampras as he was against Laver. Remember Rosewall even in his mid to later thirties was able to defeat Roche in the 1970 US Open final on grass and he was able to defeat John Newcombe in the semi before that. These are two of the finest fast court players of all time. Roche was in his prime. However on clay I think Rosewall would win a very good percentage of the matches against Sampras. It's very possible Rosewall would defeat Sampras most of the time if they played equally on all surfaces. I read about a practice set (if memory serves) Lendl played against Rosewall about 1980 or so. Rosewall was about 46 and Lendl about 20 but one of the top players in the world I believe. I understand it was a great set and Lendl won by 6-4. Now it doesn't necessarily mean anything I guess but it does show that an old Rosewall was competitive with a tournament tough Lendl. It was against a pre peak Lendl but it also was a way past prime Rosewall. I understand the rallies were fantastic from observer. Agassi used to have a lot of problems with Miloslav Mecir. He once mentioned years ago (probably changed his opinion later) that Mecir was the one who gave him the most problems. Odd thing is that according to ATP records they only played once. A player like Mecir with great mobility and the ability to control the rally apparently bothered Agassi. Mecir didn't have the biggest serve in the world but neither did Agassi although Agassi could pop in some powerful serves. I think Rosewall in his prime could very well do the same thing as Mecir did to Agassi.