I've looked up the system requirements, and your CPU being dual core, and your old GPU having 512 MB of VRAM (I'm assuming it's not the 1 GB version), placed your system in the minimum requirement category for Wow in general. Your 750 Ti has 2 GB of VRAM, so that's clearly good. Had I advised you before you made the GPU purchase, I would have suggested a EVGA b-stock (factory recertified) GTX 950 (
http://www.evga.com/Products/Product.aspx?pn=02G-P4-2957-RX ). It just went out of stock a few days ago, but they should have inventory before the end of this week. To give you a performance reference, three 750 Ti's approximately equals one GTX 970. And two GTX 950's "almost but not quite", equals one GTX 970. Also, Nvidia specifically tweaked the drivers of the GTX 950 for MMO games, as that's the card's target audience. Btw, 750 Ti's do not support SLI, but GTX 950's do.
Troubleshooting step: Download and run HWMonitor ( http://filehippo.com/download_hwmonitor/ ) by clicking green "Download latest version" link on the upper right side of page. Run the game and then determine what are the CPU and GPU temperatures and utilization? (4 pieces of information total). Also, a 5th piece of information I'm seeking is to know how much RAM your computer is using while playing this game? You can simply open task manager (hold Shift + Tab + ESC keys simultaneous -> then click "Performance" tab. How many GB listed in memory field?
Question: What was the manufacturer and model of your previous monitor? If you don't remember, could you please tell me the resolution of the previous monitor? I'm asking because I have a theory that the resolution greatly increased, which lowered your FPS.
Question: What is the precise manufacturer and model # of your power supply? Both answer are equally important in determining what graphics cards are an option for your current rig.
Addendum: I do agree that your computer was a great one when you purchased it in 2011 but that it's time for an upgrade. However, I think we should solve this issue on your current rig, so that you're in no rush to build a new rig hastily.
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notes ***
Sceptre E275W: 27" display, 1920 x 1080 resolution @ 60 Hz
http://www.newegg.com/Product/Product.aspx?Item=N82E16824112024
GPU: HIS Radeon HD 4670. 512 MB or 1 GB model?
I'll be honest, I've never played WoW, so I didn't know what Ashran was, until I googled it:
google query: what is wow ashran
google result:
http://wow.gamepedia.com/Ashran
WoWPedia Excerpt:
"Ashran is a level 100 instanced[1] cross-realm[2] "end game" world PvP zone found in eastern Draenor.[3] The name also refers to the greater Ashran zone, including the Alliance and Horde capitals, which are set outside of the PvP zone itself. The zone has a cap of 40 players per side, with multiple Ashran instances for each server".
WoW system requirements:
https://us.battle.net/support/en/article/world-of-warcraft-system-requirements
minimum requirements:
dual core (non-hyperthreaded) CPU, 2 GB RAM, GPU with 512 GB of VRAM
recommended requirements:
quad core (non-hyperthreaded) CPU, 4 GB RAM, GPU with 1 GB of VRAM