I was thinking about buying a mobo with Z87 chipset
Like ASRock Z87 Extreme4 as it is has very good price/performance ratio
What performance? A motherboard doesn't have performance. The benefits of high-end chipsets and motherboards are more sata, usb and other ports, some exclusive features, overclocking and stuff like that. But on the Haswell plaform even a cheap Z87 has the same overclocking potential as a high end one. This is just how Haswell is designed. These are not the Core 2 days when a Rampage board gives you better oveclocking than a more regular UD3. Although a high end board with better capacitors, mosfets and more phases will deliver cleaner power.
But personally if I had to buy a board for overclocking on a budget I would chose a high-quality brand like Gigabyte.
I meant price/features