Hi again sleepseek,
First of all ... way to go for getting the information

. While translating it can still be helpful and we would certainly need more information to "guess" how each may feel to you ... at least you are making choices based on something that can be "measured".
The ILD of memory foam is mostly meaningless since all memory foam is very soft (most of it under 15 ILD). Because all memory foam is temperature sensitive (softens with heat) to differing degrees ... the ILD will also change with heat and humidity so an ILD rating with memory foam really means little. Even with types of foam where ILD means something (like polyfoam or latex foam) ... a difference of 4 ILD is about the threshhold that most people can feel much difference.
The important number with memory foam is density ... not ILD. This is the most important indicator of quality. Second its temperature and humidity sensitivity, third would be how much "memory" it has (how fast it comes back) and fourth would be how breathable it is. The last three are somewhat interconnected and say more about how it feels and performs rather than about actual quality. There are many other "specs" with memory foam but these are the most important in actual use.
How firm a memory foam mattress actually feels in use has more to do with the specs of the memory foam (as above), the thickness of the memory foam layer, the body weight, shape, and weight distribution of the person on the mattress, and the layers above it (the ticking and any quilting) and below it (the support layers). Since support layers are usually polyfoam, then ILD becomes important. Density of polyfoam is also an indicator of quality (you will usually see from 1.8 to 2.4 density in the polyfoam used under memory foam). Any density polyfoam can be made to be a certain ILD so density and ILD in polyfoam do not go hand in hand.
Heavier weights, more curvy bodies, and side sleeping positions usually need a thicker comfort layer (the memory foam). If the memory foam layer thickness is not enough ... then you will "go through" the memory foam and feel the layers underneath it more. If it is too much ... then you will sink too deeply into the memory foam with your heavier parts and end up out of alignment. Denser memory foam will also tend to "hold you up higher" than lower density memory foam although again ... all memory foam in use will gradually allow you to sink in deeper over the course of the night unlike polyfoam and latex. Both of these (The Deluxe and the Gel) would likely have about 4 lb memory foam and a memory foam with gel and one without that are the same density will feel about the same in actual use with only minor variations.
Because the gel memory foam mattress has a thinner layer of memory foam on top ... you will feel the layer below it more. In this case ... the next layer down is not the 40 ILD layer they were talking about but the 2.5" of "textured" foam below the memory foam. This would likely be some type of convoluted foam which is much softer than 40 ILD. How much you felt this layer would depend on your personal "stats" and sleeping positions and the heat of your body and the room around you. It is a "transition" layer between the memory foam and the firmer 40 ILD base layer and would have a great deal to do with how the mattress felt for YOU.
With the Deluxe ... the thicker 3" memory foam is directly on top of a 40 ILD base layer because it doesn't have a softer transition layer. Because the memory foam is thicker (and will feel softer to most as long as they don't go through it) ... it may feel softer to many. If you "go through" the 3" because of your own sleeping positions, body weight, shape, and weight distribution ... then the mattress would feel very firm indeed even though the layer on top may be thicker. How it felt would depend entirely on how deeply you sink down into the whole mattress and how deeply you sink in to or "through" the memory foam. This is why what can feel firm to some would feel very soft to others.
To really be able to make a more meaningful comparison accurately for any individual (even in theory) ... you would first need the actual density of the 2 memory foams (which we don't have but are guessing are both 4 lb) and the thickness of the layers (which we have). Next you would need to know the thickness and ILD and density of any transition (middle) layers (which we don't have) and whether it was a flat foam or textured or convoluted on top (the texturing or convoluting would make the actual ILD softer than its "rating"). Finally you would need the thickness, density, and ILD of the base layers.
In addition to the mattress specs ... your own weight, weight distribution and shape, and sleeping positions would need to be known and some mattress testing and feedback with about 2.5 - 3" memory foam mattresses of a similar density and known middle and lower layers would be important.
When all of this is known ... then "theorizing" about how a mattress may feel to you becomes a possibility.
In other words ... it is all about how every layer of the mattress interacts with every other layer and with you and your sleeping environment. Just knowing about the memory foam itself will only give you a little piece of the puzzle.
Because most side sleepers or average to heavier people would feel more of the transition layer under 2.5" of gel memory foam (especially because it is only 4 lbs) ... it would feel softer (because of the softer transition layer) than those who "went through" the 3" layer of the Deluxe 4 lb memory foam which has very firm foam under it. Those who didn't go through the 3" of the Deluxe and feel the very firm foam underneath it as much would likely think the Deluxe was softer.
Of course all of these are less durable and will likely soften more ... and more quickly ... than higher quality and density memory foam so how it feels for the first few days will change over the course of the first few weeks and/or months of use.
Phoenix