Just my two cents...I have met Arnold twice...Once at a grand opening of Planet Hollywood ( just a "Hi,nice to meet you")the second time at a gym that I was training at in Newport R.I.. He was there filming a part for True Lies. Arnold is not 6'2". He is 6'. And , he is not particularly large framed. However...
In regards to him benching 500, I would think absolutely. Not that I can do it, but it is not that impressive. There are a half a dozen guys in my gym that can do that, and I know for fact 2 of them are naturals. Arnold was the "freak" of his time, and I would think that some good strength came with that size.