what do you suggests if we want to achieve something around 1.5 terahash/sec?
thanks
To do those speeds, it be more realistic to get the next batch of ASIC's coming out.
To compare GPU wise you'd need 2000-2500 Radeon 7970's. I'm not sure I want to figure out how many Nvidia cards that would be, but most likely just multiple that 2000-2500 by 4-6 depending on which card you get. Buying 10,000+ GPU's will cost way more than it's worth ($3 Million).
However an Avalon ASIC, running at around 60-65 GH/s ($1300-1500), would mean you'd need around 20-25 of them to get to 1.5 Th/s.
Clearly it is more cost effective you can buy ASIC's.
If you haven't actually bought the CUDA cards yet ( you said nearly yes), I advice you do not.
Unless you actually have another reason to buy CUDA cards, outside of bitcoin mining.
I know CUDA cards, are very popular in Render farms and simulation programs, but these are not good choices for Bitcoin.