I think so, he has defeated 11 current(at the time)/former heavyweight champiopns, 2 olympic gold medalists and some good pros with strong amatuer world championship performances(ibragimov and chagaev), His 2nd reign lasted 9 years :S and he held a title belt before that too. He also made great efforts to get the other champions in the ring too, offering ibragimov and haye 50/50 splits to make teh fights happen..I would say certainly top 10 all time, not top 5 for me due to too many bad losses.