Overclocking
There are a few different ways to overclock on the X99-A motherboard. The easiest way would be through the AI Suite 3 software. You can run their 5-way optimization, which has quite a lot of options.
Once completed it will give you your optimization report. For our system it gave us a 30% overclock bringing our Core i7-5960X up to 4308.6 MHz. Not bad at all.
ASUS also has built an easy tuning wizard into the BIOS. While it does not have as many options it simply asks your questions about your current setup and provides a nice overclock on both the memory and CPU.
Of course for our max overclock we went into the BIOS ourselves and did manual overclocking. Bumping the CPU voltage up to 1.4V I was able to bring the system all the way up to 4.4 GHz. Anything after that and the system would boot, but not be stable.
As you can see it looks like 4.4 GHz is the highest overclock we have been able to achieve on the X99 platform on all of the motherboards that we have tested.