Little problem with your math. Even tho your push plate will be 15.5 long, you are not applying that entire width to your flange. Only thing really putting pressure is the part of your slide that is going under your beam flange. Assuming the 2 in the 15x2 is actual contact under the flange then our math may be correct. Of course the longer the slide the more the force is spread out and the least likely the slide will cock to one side or the other. Where I think your math may be wrong is the height of the push block. The taller the pusher, the more leverage it would exert on the base multiplying the forces. From personal experience, due to the low tonnage output of your combination of previously mentioned pump choice, hp output, and cyl size, and slide lenght, a 1/2 thick flange will probably be plenty strong enough. On the other hand, if you do go with a different power and pump source to reach maximum yield, I still think your ibeam will bend, bow, and twist until it fails.
to answer your question of wedge material, I have used just cold rolled steel for several wedges and never had a failure. One way to reduce the force exerted on your beam would to be to use a narrow knife wedge design instead of a spreaer type wedge. I find a knife wedge will slice thru knots with little effort, while a speader wedge is trying to pull that knot apart and takes more power and pressure to do so. I really think a combination of a knife and spreader wedge would provide the benefit of low initial contact pressure and still provide the spread for faster splitting. Making the leading edge of the wedge long and narrow before starting the spread of the wedge I would think would make splitting easier.
Also you cant compare the processor high flow multi pump engine setup with a single flow gear pump. While the processor is capable of pumping the 40 gpm and is being pulled with just a 35hp engine, it is a multiple section pump with each section providing fluid for separate operations. Since all operations usually are not working at the same time, nor do they all require maximum pressure, the engine is not supplying 40gpm at full pressure, some of that oil is simply recirculating at very low pressure and not doing any work until needed.
