A full bolt-on Explorer can easily run in the 500–550 whp range, depending on the dyno.
The number one limitation is the fuel system, which can barely support an ethanol blend between E30 and E40 (I still don’t know why they call it E50). If you want higher ethanol content, you need to upgrade the fuel pump and injectors. On the F-150 platform, the engines are both DI and PI, so they can make about a quarter of that cost just by improving the fuel system, while on this platform you have to budget close to $5,000.
The other two limitations are the transmission, which is rated at around 600 lb-ft of torque and is already at its limit, and the turbos.
Anyone aiming for 600 whp should expect to spend around $10,000, just to put a number on it.