Too large for pony? I don't now exactly, but I am about 65 kilograms (I cannot put myself to find out counting with pounds...) and height about 165 centimtres. I ride little pony, she's to my bust and not xet well-muscled. And she's fine. Yfrog - img0622a
I think it whole depends on each pony, how is he tall/strong/used to/muscled and if he is all right (not bad hooves, spine,...)
And ponies may not seem like this, but they are very strong. I am not telling you to ride on falabella, but ponies in type of hucul, cob, hafling, fjord, they are more then OK to be ridden by tall men, even in western saddle, which is about 10 kilograms more.