To put in efforts near ones they would have near their optimum fighting weights. Danny Williams seems to of made a career out of this, fighting at 270 pounds and somehow not looking fat and or overly "soft" around the midsection. Bowe, of course. Though he eventually paid for that. Tubbs, obviously.
Tony Galento was a formidable threat. Especially at heavyweight, being fat can look worse than it really is. It does not really diminish punching power (in fact, often they're hard hitters) and while they're less mobile, they have some padding to take bodyshots. David Tua was pretty good too.
Brian Nielsen: He didn`t even look like a fighter which made almost all his opponents underrate him and it worked to his advantage. He didn`t have the biggest punch but was a very good body puncher and he was tough as nails.
lionel butler. garing lane. frankie swindell. big bad leroy jones. the list is endless. obese looking fighters that actually have great conditioning and speed. i have always found that amazing.
Irish cruiser weight Darren Corbett. Started his career as a heavyweight, weighing as much as 226lbs. Then moved down to cruiser where he had some sucess winning the commonwealth title. Eventually moved to his natural weight at light heavyweight but wasn't the same.
Greg Page, Tim Witherspoon, Tony Tubbs, Garing Lane, Liolnel Butler, Bowe, James Tillis eventually, Kirk Johnson, James Broad.