"2 x ECS NBGTX460
GeForce GTX 460 SLI configuration, 1 GB GDDR5 per card"
ECS NBGTX460 linkhttp://www.newegg.com/Product/Product.aspx?Item=N82E16814134117
as for the bottleneck i suspect it would however am unable to find benchmarks for proof with your specific chip. i believe you would not bottleneck one but once sli is in the mix you'll be hindered. however as a next upgrade path for later mobo/cpu/likely ram they's be a good jumping off point... also make sure your psu can handle it, what kind of psu do you have
i cannot reccomend the specific card they used, ecs. while it is a good card with a good cooler they really need to brace the pcb as there are many reports of bent pcb boards from to much weight by the massive cooler his will cause failure over time