You're starting this off with a bad concept, cheap. When it comes to overclocking, cheap isn't always the best idea. You get what you pay for.
The minimum cost for a Z87 or Z97 board would be around $120. That's where the ASRock Z97 Extreme4 and Asus Z97-A are priced. They have the proper cooling and the PCIe slots are designed for SLI/CF. For SLI you will need a board that supports x8/x8 speed on the PCIe slots. If the board only support x8/x4 slots, forget SLI. The x4 slot will bottleneck the second card. It will work for CF but not SLI. So the Pro4 is out.
You will want to purchase the Z97 board. It has more advance features and will support Broadwell Chips.