Overclocking DRAM on MSI Z97 Gaming 5

Question

Hello again 
Since I am pretty new to overclocking, I'm having some fun adjusting clocks of my hardwares, this time my Kingston HyperX modules which were reviewed as having a good OC capability. I performed some tests using AIDA64 Extreme software: memory read, memory write and memory waiting time. I tested stock 1866 MHz frequency and then I overclocked it to 2400 MHz. Here are my results:
Kingston HyperX 2x4GB 1866 MHz 10-11-10-30-1T
Memory read: 26.981 MB/s, 26.994 MB/s, 26.966 MB/s
Memory write: 27.234 MB/s, 27.270 MB/s, 27.346 MB/s
Waiting time: 52.9 ns, 53.1 ns, 52.6 ns
Kingston HyperX 2x4GB 2400 MHz 13-15-13-39-2T
Memory read: 32.800 MB/s, 32.899 MB/s, 33.127 MB/s
Memory write: 33.778 MB/s, 34.439 MB/s, 34.124 MB/s
Waiting time: 51.3 ns, 52.0 ns, 51.1 ns
Seems like adjusting memory clock to 2400 MHz frequency indeed improved memory's read, write and waiting times. Voltage increased from 1.5V to 1.68V.
I also tried with 2600 MHz, but the results in AIDA64 were worse then on 2400 MHz and even worse then on 1866 MHz.
-According to this, I believe 2400 MHz memory frequency is a maximum that my kits can be pushed, if higher frequency caused performance drop? Perhaps I could adjust higher voltage manually? Motherboard changed timings and voltages automatically.
-Are these results good? I have never overclocked memory before.
-I guess even though results show higher values of reads and writes, there won't be any difference I can actually feel?
-And last question: how do I check if memory runs stable on adjusted frequency?
MSI Z97 Gaming 5 makes DRAM overclocking totally easy as it seems!
Thanks in advance 

Answer 1

I can see the description of my RAMs, on the package, it says 1866 MHz, it already was 1866 MHz out of the box when I firstly plugged them.
Otherwise there wouldn't be 1333/1600/1866 MHz variants right? 
Anyway, is that a good overclock?