Hi Hobotrader,
40 ILD Dunlop would be firmer than most innersprings. Polyfoam also comes in many firmness levels and some of them have much more give than others. Different types of polyfoam (HR vs conventional for example) can also make a big difference.
Latex innerspring hybrids can be a very good design for many people but like any other combination of materials the key is always in the design and layering that provides the best PPP (Pressure relief, posture and alignment, and Personal preferences) for each individual person. Which innerspring and which thickness, ILD, and combination of latex is just as important as the components and materials themselves.
Your design theories are far outside of any “typical” construction I know of and your changes are also rather “random” (and in some cases making assumptions that may not be accurate) so I’m not really following the “theory” or logic behind what you’re doing. Trial and error may be necessary with this approach.
While most springs may not be as firm as the Dunlop … they do have a different compression curve and some people do better with them. Post #16 here and post #2 here talk more about this.
The polyfoam at the bottom would have the least effect of all the layers because it’s the furthest away from you and ultra firm polyfoam on the bottom wouldn’t be much different from having the latex directly on a foundation or on the floor.
That’s the truth … but the trick will be getting it right in the first place 
Phoenix