Anything over 2666 is technically an overclock, and not guaranteed to work. That said, I'd really expect you to be able to get a lot more than 2300 out of that RAM if its XMP says it can do 4100.
Have you checked whether your BIOS is the latest version?
Is the RAM from a reputable vendor? It could just be that the XMP profile is wrong (in which case you'll need to configure the timings manually).
Without further testing/experimentation, it is impossible to say whether the limiting factor is the RAM, the motherboard/BIOS, the memory controller (in the CPU), or some combination of the three.
Nostalgia isn't what it used to be.