Well, that's all well and good, but if, say, the hashrate went up to a nice 1.65PH/s (an average of your two extremes) the difficulty would be a nice 213,125,000,000 (rough estimate of course). That would mean at an exchange rate of $200 a coin, you'd be making a sexy $10.33 per year with your $1300 Single SC....losing it all to energy costs (or if you have free electricity, it would only take 126 years to break even).
But on the bright side, if that Single was $1 it would take just over a month to break even.
My point is that something has to give in order to support high hashing rates.
Yep, I think I mentioned that. The mining equipment is going to have to become cheaper, more powerful, or both. I fully expect a Single to pay back 2-3x (maybe up to 7x if things go nuts, or I lose that particular shirt) in the next 12 months but that is 80-90% of the BTC that it is ever likely to mine. It's trash (for BTC at least) in less than 2 years almost guaranteed.
The exception to this would be a skyroketing price that takes the block reward from $250 (assuming the price keeps falling to hit $10 today) to $5000 ($200/
BTC) over 12 months. This would mean that a bASIC could be earning about $96 in January in (@$8.82/BTC) , but $220 in December (@$200/BTC), even though the profitibility in BTC has gone down by 90%. Assuming that this major price swing didn't impact difficulty even further.
I doubt such a thing will happen, but even if it does the exact scenario above will not play out since a LOT more mining gear will be able to be sold every for every block generated. Instead we will see shorter ROI cycles and more frequent gear purchases required to keep up with all the other folks who are getting "rich." I have been thinking about putting together an ASIC shipment model based on the value of bitcoin which would allow me to get more accurate, but until then I'll just have to say that I
deduce that we would see difficulty spike up to something like 600-800M and 12 month ROI on a $700,000 miner the size of a refrigerator that consumes 10KW (well maybe with $1000 BTC)
I think that the easiest formula I have seen to capture this is a "Spend half my income on upgrades" model. After block halving this means that each month each miner will have a portion of a bit over
BTC100,800 so if we add in the 50% rule we get ~
BTC50k spent on mining equipment. At $10 this is $100k/month, at $200 this is $2M/month, at $1000 it's likely $5M/month,assuming more than 4 years to get there.) It's easy to do this with constant increases and an easy forecast just by adding mining capacity with a 2-6 week delay for ordering/shipping. Unfortunately the reality is to be useful it will require a basic P/L forecast analysis for every time period to see if it is a buy or hold period for hardware, hmmm.
Until ASIC at least comes out and we see the first difficulty change or 2 I'm going to stand pat, and continue to calculate on BTC based ROI. Any fiat based bonuses I get due to exchange rate are awesome, but I'm not counting on them.