Lendl is even frank enough to admit it. He could only beat Chang and Wilander half the time in his prime. Beating Federer would just be a fantasy.
Here's Lendl's head to head against Wilander and Chang from the ITF website.
Versus Mats WILANDER (SWE)
Year Tournament Round Surface Winner Score
1982 French Open 16 Clay (O) M.WILANDER 6-4 5-7 6-3 4-6 2-6
1982 U.S. Open 16 Hard (O) I.LENDL 6-2 6-2 6-2
1982 Barcelona QF Clay (O) M.WILANDER 6-7 1-6
1983 Brussels Indoor SF Carpet (I) I.LENDL 7-6 7-6
1983 Cincinnati SF Hard (O) M.WILANDER 0-6 3-6
1983 U.S. Open QF Hard (O) I.LENDL 6-4 6-4 7-6
1983 Australian Open FR Grass (O) M.WILANDER 1-6 4-6 4-6
1984 World Team Cup Clay (O) I.LENDL 7-6 7-5
1984 French Open SF Clay (O) I.LENDL 6-3 6-3 7-5
1984 Davis Cup 1984 Clay (O) M.WILANDER 3-6 6-4 2-6
1985 Monte Carlo FR Clay (O) I.LENDL 6-1 6-3 4-6 6-4
1985 World Team Cup Clay (O) I.LENDL 6-4 6-3
1985 French Open FR Clay (O) M.WILANDER 6-3 4-6 2-6 2-6
1985 Tokyo Indoor FR Carpet (I) I.LENDL 6-0 6-4
1986 Lipton-Boca West FR Hard (O) I.LENDL 3-6 6-1 7-6 6-4
1986 Masters SF Carpet (I) I.LENDL 6-4 6-2
1987 French Open FR Clay (O) I.LENDL 7-5 6-2 3-6 7-6
1987 U.S. Open FR Hard (O) I.LENDL 6-7 6-0 7-6 6-4
1987 Masters FR Carpet (I) I.LENDL 6-2 6-2 6-3
1988 U.S. Open FR Hard (O) M.WILANDER 4-6 6-4 3-6 7-5 4-6
1994 Sydney 32 Hard (O) I.LENDL 6-2 6-1
1994 Coral Springs 16 Clay (O) I.LENDL 6-3 4-6 7-5
Ivan LENDL (TCH) Leads Mats WILANDER (SWE) : 15 to 7 *
Versus Michael CHANG (USA)
Year Tournament Round Surface Winner Score
1989 French Open 16 Clay (O) M.CHANG 6-4 6-4 3-6 3-6 3-6
1989 Masters Carpet (I) I.LENDL 6-1 6-3
1991 Grand Slam Cup SF Carpet (I) M.CHANG 6-2 6-4 4-6 6-7(5) 7-9
1992 Cincinnati SF Hard (O) I.LENDL 6-3 6-2
1992 New Haven QF Hard (O) I.LENDL 6-3 7-6
1992 Long Island SF Hard (O) I.LENDL 6-2 6-3
1992 Tokyo Indoor SF Carpet (I) I.LENDL 6-3 6-4
Ivan LENDL (TCH) Leads Michael CHANG (USA) : 5 to 2 *
I'm not sure exactly how Lendl would do against Federer on hard court. I would tend to favor Federer but Lendl himself said that with the rackets today he could do more from a defensive position than in the past. As far as the racket speed is concerned, I think often Lendl wasn't necessarily going for great power in those days but depth and control against some player but he could unleash shots with great racket head speed and power if he wanted to.
Bear in mind that Lendl did quite well against a young and powerful Agassi in those days and I think overall that Agassi, off both sides could hit with as much power as anyone today. Lendl handled Andre's power at the US Open a few times also. However to be fair Agassi wasn't at his peak yet.
Brad Gilbert, who played both Agassi and Lendl thought Lendl hit the ball harder than Agassi but Agassi's ball come back at you faster because Agassi hit it earlier.
Another point is that we all forget about what a fantastic serve Lendl had and it would be very hard for anyone to break Lendl on a hard court.
Versus Andre AGASSI (USA)
Year Tournament Round Surface Winner Score
1987 Stratton Mountain SF Hard (O) I.LENDL 6-2 5-7 6-3
1988 U.S. Open SF Hard (O) I.LENDL 4-6 6-2 6-3 6-4
1988 Masters Carpet (I) I.LENDL 1-6 7-6 6-3
1989 TOC Forest Hills SF Clay (O) I.LENDL 6-2 6-3
1989 Canadian Open SF Hard (O) I.LENDL 6-2 3-6 6-4
1989 U.S. Open SF Hard (O) I.LENDL 7-6 6-1 3-6 6-1
1992 Canadian Open FR Hard (O) A.AGASSI 6-3 2-6 0-6
1993 New Haven QF Hard (O) A.AGASSI 3-6 4-6
Ivan LENDL (USA) Leads Andre AGASSI (USA) : 6 to 2