First things first, 14 days difficulty requires ZERO increase in difficulty. Difficulty increase occurs when block rate occurs faster than predicted average should be. 50% difficulty increase requires ~7-9 days between difficulties.
7-9, days. Ok : ) So could be that 6 difficulties pops up in early August.
Next, the fact is that these analysis make no sense because a static difficulty increase makes 0 sense. Retargets have been at 50% for... 1 difficulty change. Before that it was a 25% retarget. Before that 65-75%, before that 40% before that 30ish%.
Not to mention a static PERCENTAGE increase means an exponential numerical increase (of difficulty/hashing power). This is completely unfeasible unless price continues to rise at a similar rate.
I agree price is a factor, but there are a lot of GPU's out there with bored users, that don't need a lot of incentive to just point unused cycles at the network. Users like me for example. Widespread media attention (the hacking of the 25k coins, the acceptance of BTC by wikileaks, MtGox articles, etc) will only bring new users onboard who don't need to invest much if any capital to continually double the hashing power of the network. I am not saying it is bad, but I completely disagree that it is unrealistic.
In fact, in 2 difficulties it is likely your analysis will fall through like a brick on a wet paper napkin. Next difficulty is set to bump over 1million difficulty, but price has just fallen through the floor to around $13 (probably end at $10 or so). This makes mining a complete flip of the $30 / coin 500k difficulty point at which all the machines that are coming online now to bump the hash rate up were bought. Some people will try to stick it out because they sunk their money in so foolishly, many people will run up a massive sell-off to try to recoup the losses they suddenly find themselves taking.
Yes, foolishly. I agree, given my analysis and your input that doublings/retargets could occur in 7-9 days instead of 14. Unless 1.0Ghash mining 20-35BTC breaks even in terms of USD, those mining rigs don't appear to be the greatest investment. Right now (15 USD) 35BTC recoups $475 or so. At $20 USD they recoup $700. At $30, might be break-even. Hopefully price rises, and more people discover bitcoins.