My CPU is Pentium G2020 running on Gigabyte H61M-S2P motherboard with 8GB DDR3 ram. I want to upgrade for faster rendering without adding additional RAM on my machine or changing the processor. Please suggest a suitable graphic card.
For the record, RAM doesn't affect render times. If you would like to know which graphics card you should buy for rendering, i suggest visiting http://blenchmark.com. Here you have a full list of all the benchmarks on almost all the consumer CPUs and GPUs.