There is no perfect yak for you. I think you're going to be disappointed because you're not going to get what you want parameter wise. Ocean Kayak makes the Big Yak which is 9' 8" long, 34" wide, but it's maximum carry capacity is only 300#.
http://www.oceankayak.com/kayaks/single_kayaks/big_yak.htmlIf you want more weight carrying capacity, you're not going to find it in a 9' or 10' sit on top fishing kayak. More carrying capacity for weight means a longer yak. Two yaks are below.
Ocean Kayak makes a yak called the Prowler Big Game. It's 12' 9" long, 34' wide with a weight carrying capacity of 600#.
http://www.oceankayak.com/kayaks/angler_editions/prowler_big_game.htmlAnother "big guy yak" is a Cobra Fish N Dive. It's 12' 6" long, 36" wide with a weight carrying capacity of 600#.
http://www.cobrakayaks.com/kayaks/cobracat4.htmlKeep this in mind. These yaks weren't designed for standing. In the end, you're going to have to compromise on your parameters (what you want) if you want to fish from a yak.