Intel Extreme Tuning Utility is a performance tuning software for novice and experienced enthusiasts to overclock, monitor, and stress a system.
The software interface exposes a set of robust capabilities common in most enthusiast platforms and special new features available on new Intel processors and Intel® motherboards.
Intel Extreme Tuning Utility Features:
System Information – Inspect processor, memory, graphics, BIOS, operating system, and motherboard information.
Basic Tuning – Simple three-step process: benchmark your starting performance, overclock your processor, and measure your new performance and witness the performance unleashed!
Advanced Tuning – If you are an experienced overclocker, we give you all the controls to maximize the untapped performance of your processor, memory, and graphics hardware.
Stress Test – Interested in how stable your overclock is? The included stress tests help you test your system to be sure.
Benchmarking – Would you like to see how your setup compares? With Intel® XTU, you can benchmark your system and then compare your scores online with HWBOT.org.
Application and Profile Pairing – Have you optimized the overclock for a specific application? Use the app profile pairing feature to apply different overclocking settings to separate applications.
Intel Extreme Tuning Utility
Which Is this better bios overclocking or this?
Definitely BIOS, because XTU only applies after booting in OS.
always bios .,.XTU is good for fast "testing" in windows
but most time is loaded bad setting
it also depends on MODE for XTU -XTU inference ON/OFF in bios
OFF mode is post boot emulation ,on - direct "similar like bios"
bios is best ,…,or sometimes verify XTU
XTU benefit ?? .,.easy access/controls .,contains some stress levels ,…,profiles
but full OC support is only BIOS 
For testing using XTU is really good. After finding a balance best to do is bios overclock so no matter which os you bootup you can always get the same outcome without worrying about setting things up again