Hi filterflyguy,
Both of these mattresses have quite different designs and use different types of latex with different layer thicknesses and different covers and possibly a different firmness level for the base foam as well so there wouldn’t really be a firmness level that “matched” one to the other because even if the top layer of latex was a similar firmness level in both of them comparing them would be more of a subjective comparison and different people would probably have different opinions about how closely they matched depending on their body type and how deeply they sink into each mattress.
Having said that … the US mattress site rates the Newness as a “7” on a scale of 1 - 10 and while these types of firmness scales can vary widely and are notoriously inaccurate when they are used to compare mattresses … something in a similar firmness range on the softer end of the scale would probably be somewhere in the ballpark.
If someone at Dreamfoam is familiar with the Optimum Newness their guess may be more accurate but either way I would make sure that you talk with them about your firmness choice so that they can provide some some guidance about what others with your body type or sleeping positions would often do best with based on “averages”.
I would also keep in mind that the Eurotop has the option to exchange the comfort layer for a different firmness level so you would still have the option to customize the mattress after a purchase if your initial choice was either too firm or too soft for you.
Just in case you weren’t aware of it as well … if you purchase either one from the Dreamfoam website there is an additional 10% discount (see their facebook page here) and you would also have the benefit of their 45 day comfort guarantee on your purchase.
Both of them are high quality/value choices but the Eurotop would be a little less risky because of the additional options that are available to you.
I don’t know how drilling holes would affect the strength or integrity of the foundation but if you have a solid surface foundation and you wish to add some ventilation under your mattress (see post #10 here) to reduce the risk of mold and mildew and moisture retention in your mattress then it may be worthwhile adding a bed rug on top of the foundation instead of drilling holes in it.
Phoenix