850,
I'm not telling you that you shouldn't get the high HP splitter, but don't think in any way that a 5hp 11gpm 22 ton splitter is in any way "underpowered". 5hp will split any piece of wood that you can muscle up to it.
The bigger, more powerful splitters are bait for the "Tim Taylor" crowd... and that's straight from the mouth of a commercial splitter manufacturer rep!
Now, if you start talking about 4-way wedges and stuff like that, then, yeah, you might need a little more power... but aside from that, 5hp will do everything that 15hp will do, and do it a lot cheaper. And, unless you have a multi-person team operating the splitter, cycle time really isn't a factor in my experience... my 5hp splitter is waiting on me MUCH more than I'm waiting on it.
Just my experience, your mileage may vary