My intention for the newegg link is to illustrate the PCI-e slots.
Regarding PSU sizing:
Overclocked! GPU, 1200W++ on synthetic loads!
Real World Trifire 7970 Power Consumption Recordings. - AnandTech Forums
Long thread on OCN:
Trifire 7970's...1050w Enough?
Gaming will draw substantially less compared to synthetic, especially when the CPU is the bottleneck. Since you are doing mining, your load is most likely closer to synthetic loads.
One config at Hard. Synthetic benchmarks can drive power draw past 1000W.
Real world power consumption measurements from triple 7970's
The values are drawn from the wall, so efficiency must be factored in. Plus, kill-a-watts are known to give inaccurate readings. I don't know how well coin mining software loads the GPUs. If they load them like benchmark software does, then a high quality 1200W is probably a necessity.
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With regards to buying from Newegg or Amazon:
Why SIngapore retailers or distributor charging us a premium?
I've not done it myself, but some use VPost, though I've never done it before. Yes, there is the shipping, which may negate any price difference. The other issue is with warranty and RMA.
BTW, Newegg is not the cheapest in the US, since physical stores like Microcenter (and maybe Fry's) are known to sell cheaper.
According to the VR zone thread I linked, you can get cheaper hardware from Malaysia or HK.