Good pic.
There are also fatbars, similar to axles, but they're rolling, and slightly easier to handle because of it.
Bottom line is: Use a thicker bar, that way you won't have to load the bar with extreme weights.
I believe that grip training should have as little effect as possible on the regular training, and if you're doing bar holds with a regular bar, you will have to go fairly heavy, even if you use an over/over grip.