I need to defend Royalty here.
I don't think he was speaking about specific contests for Ronnie. Gunter was customarily around 300-lb. He was 285-lb as far back as the 2000 Mr. Olympia, and even going back before then, he must have been 275 or 280. Maybe in 1994 he was 260.
As far as Olympia showings go, Gunter was 295 in 2002, and 300 in 2005. Ronnie was 287 in 2003 and 296 in 2004. Someone from Getbig - could have been Hulkster - asked Ronnie via e-mail in 2004 what his weight was at the British Grand Prix. It was something ridiculous like 304. I would have remembered it if it was 305 or more. It was either 302 or 304. At least that is what Ronnie claimed.
Gunter himself stated that he was 6'1.5" in the BFTO 2000 VHS/DVD. Ronnie Coleman was often pegged at 5'11, but I think that was rounded up from 5'10.5". However, he is not that height today. I would be surprised if he was 5'10 barefoot today, but I am 5'8.5" and have been around pros many times, and it has been my observation that while some of them have lied about their weight before - Dexter Jackson being 235, but skipping every Ironman weigh-in, lolz - pros rarely lie about their height.
I also have big hair and wear a shoe with a nice sole so that I look more like 5'9.5" in public, so I judge the height of pros based on that height. Ronnie appeared to be around that height or a bit taller in the years I saw him (2007 to 2014). Gunter was and probably still is just under 6'2.
And to Royalty's point - yes, both competed around or at 300-lb at different contests in their career. At the 2004 Mr. Olympia, Ronnie was 296-lb, and Gunter was at least that.