If I remember correctly K80 memory is actually 24GB, not 2x12GB. This is a pretty important distinction in this context (training GPT-2).

Also, you can get at least 6 K80s for the price of a single RTX Titan (also 24GB). So it would be faster (I don't think RTX Titan is 6x faster than K80) and 6x more memory for the same price. It's a very good deal.