Looking to upgrade my 650 Ti for 5-boxing. Instances are fine right now, but OMG cities and garrisons are horrible! What's the current sweet spot for GPUs assuming I'm not looking to go ultra graphics w/ lowered FPS in background.

Other specs that might be relevant:
- 16 GB RAM
- i5-2500K Processor 3.3GHz 6 MB Cache Socket LGA1155