How can I tell if my current spec is bottlenecking?

[Wireframe2]

Case: Corsair Carbide 300R ATX Mid Black
CPU: Intel i5-4590 Haswell Quad-Core 3.3GHz
Motherboard: ASRock Extreme4 Z97
RAM: Team Vulcan 16GB (2 x 8GB) DDR3
GPU: GIGABYTE GTX 970 x 2 (SLI)
SSD: Crucial MX100 SSD 256GB
HDD: WD Blue 1TB 7200RPM
PSU: Antec HCG M Series 620W 80+ BRONZE
Disc drive: LG GH24NSC0B
Adapter: TP-LINK TL-WN881ND
OS: Windows 8.1 Home Edition

Monitor: LG 22M34D-B 22" x 2, Acer GN246HL Black 24"

Title. I just want to make sure I'm getting the most out of my components before I consider upgrading.

 

[Hawkshot]

That CPU will not bottleneck sli 970's so don't worry about that, you shouldn't need an upgrade for a while yet