Hi,
 
Not sure if this is the right place but anyhow, I would like to buy an second GTX 970. However, I'm would like some feedback whether or not my system can handle it. Since I just bought the first one and sometimes I get the feeling that my computer already has a hard time.
I currently have:

• Asus Sabertooth Z87
• Intel Core i5-4670K
• GV-N970G1 GAMING-4GD
• HX Series HX750
• 16 GB Geil RAM
• Kingston 128 GB SSD
• 1 TB + 2 TB + 256 GB + 256 GB + 600 GB HDD

Also the reason for buying a second GTX 970 is that I would like to have 144 Hz on my Nvidia Surround (3x Asus VG278HE). Resolution I have is 3420 x 1920. I assume this is possible with 3 DVI-D cables, already worked on my previous GTX 770 SLI, but some conformation would be nice.
 
Thanks in advance.

Ya I know what you mean but its always the motherboard and the CPU you need to know if you have a 3rd generation up CPU and MB. 3rd and up that's all you need to have. to run any card PCIe 3,0 its about the same bandwidth as your other so you'll be just fine. I still use 3rd gen 1155 socket setup with 3 760s and a 780 for PX. Had to add a PSU (making sure to ground the PSUs to same metal.) to my setup but having the right adapters and info is good.
 

Your PSU and components should be able to handle this