I disagree (sort of)
I have a Canon 40D with the standard 28-135mm lens and it was more than adequate for safari, with the possible exception of a few opportunities for birds where 200mm would have been better. More important is where you go on safari. Some game parks (especially, in South Africa)restrict the vehicles to paved trails. Look instead at private game reserves like Nkorho Bush Lodge that border the Kruger National Park in S. Africa but are more liberal in going off-trail when tracking leopard and such.
I saw people with mounted cameras that looked like telescopes, but that's extreme. Who wants to carry that gear around unless you're a working pro.