This goes beyond my knowledge and experience with hydraulics. I troubleshoot and fix existing systems made by people much smarter than me, never designed or thought about making a relief but based on hyd principals the ideal relief would be a needle type seat.
Just like cylinder diameter and surface area effects the amount of power generated , so does the smaller the surface area of a relief needle valve effects the strength and sensitivity of a relief and better for that cracking pressure type operation.
Like I say.... Beyond my pay grade but that's how I see it
. Nice thing is you already know flow rates and the amount your dealing with and I wonder if there's a formula out there that would tell you port size and needle dimensions to get what your looking for?
Hmmmm, i might be able to get you a pilot relief valve that runs at about 350psi come to think of it! I'll let you know next week.