How much HP can you put to a Teleflex Rack type steering set up with a brand new Bravo 1 drive saftley?

I have a 496 Mag and I am going to do some internal upgrades and bring it up to 500HP-525HP. I feel I may be limited by the steering system not being a Latham hydraulic type.
What are the potential mechanical problems, then of course resulting in saftey issues?

Thanks,
Robb

Your cable helm is not really the problem as it drives an internal power steering piston. The stock steering piston is connected to a tiller arm within the gimble.
I'm not so sure that it is really about how much HP you've got but more the size, weight, and speed of your boat.
It is commonly suggested that boats that go over 65mph should have at least an "add on" external steering system. This means that an external steering piston is controled by the stock Merc power steering system. A "full" external sytem would require a new helm...