You wouldn't need 6GB. The latency on main memory for a GPU is horribly bad so bad that any process which needs random access to GPU main memory will be annihilated by a CPU in terms of performance. GPU memory is designed to stream textures and as such it couples massive bandwidth with extreme latency. Scrypt was designed to fill the L3 cache of a CPU. The developers of alt-coins had to intentionally lower the memory requirements by 99% to make GPU competitive. Yes Litecoin and clones use about 128KB of cache. The MINIMUM memory requirement for Scrypt is 12MB. It doesn't take 16GB. Try it out yourself or check out various hacking forums the OpenCL performance for Scrypt (2^14, 8, 1) is beyond pathetic. A cheap CPU will run circles around it.
Some interesting stats here -
https://github.com/floodyberry/scrypt-janeIf I'm reading these correctly, they confirm my tests that it takes about 2 seconds per hash per GB memory required on a modern processor.
Interested to know what you think would be a good memory requirement/time tradeoff to resist GPUs but maintain a good block validation time.
One could even design the algorithm to become more memory hard over time (i.e. double memory requirement every 2 block years).
Yacoin? Nfactor started a little low though.