You may be misinterpreting some things...
"40nm RSX MOD" is not something you do "to get better temperatures"...
I dont understand what you are trying to compare. If your machine is fine, you dont need to do anything. This is not some kind of "upgrade". This is a last resort repair path.
If you are trying to get a "quiet" machine and are considering the 40nm RSX, you may get disappointed too because normally is not about the RSX getting "hot". It is always about the CPU anyway.
In that case, the answer is yes. You can most definitely get OK temperatures without "40nm mod". You dont need 40nm for that.
Standard machine can run cool too, even without modifications. CPU may need delid one day but RSX normally doesnt even need it.
PS:
When you delid both, this is what you normally see:
View attachment 36901
In a normal machine,
The CPU has lost almost all contact with the IHS while the RSX is completely fine.
What this means in practice, is that the Fan speed is pushed higher and higher by the hot CPU to try to compensate for the poor thermal transfer, while the RSX is OK.
This indirectly makes RSX run even cooler than normal, even in machines that were never opened or maintained. You can check this yourself.
In fact often when people mess with them, is when things get worse, not better especially for RSX. Or like in this case, get very small or no improvement.