Generally, to maximize plat generation, you want to find the hardest thing you can kill as quickly as possible, as swarmy as possible.
Since you have high skinning, I'd recommend something skinnable (I know, it's obvious), and doing several arranges each time. I'd also suggest something that drops coin/treasure, as you're going to be plowing through thousands or hundreds of thousands of critters, and you can make 500 plat off a map, or some decent change off a scroll, and the gem/coin drops aren't anything to sneeze at.
I'd go so far as to say, for pure plat-per-hour generation, not concerned about skills, just maximizing coin, don't bother with locksmithing, especially since it's 200-400 ranks below everything else, it would just slow you down, and the boxes you could pick are well below your economic range.
At a much, much, lower rank than you can hunt, I'd say quartz gargs are awesome, but they stop mid-200s. If you're 400-500-600 in combat ranks...Gryphons? I'm honestly not familiar with combat once it breaks over the 200-300 range. I plugged this in to the bestiary on elanthipedia, and saw warklins and black marble gargoyles as well (though those stop at 375 and are cursed).
Personally I'd avoid anything undead, and flat out wouldn't hunt non-corp unless you have a pet cleric to continually drop 200+ count blessings on your weapons.
One thing I'm not sure of, and hope someone can tell me, is whether it's more grossly efficient to hunt pure skinnable critters, if you have extremely high skinning and can pull off max perfect arrange, when compared to a skin/coin critter. I'd almost assume the pure skin could reach higher values.
I'm a badger, I be badgerin'
