here's how I justified it. Say you use your new air for 2-3 years. Say you spend around 20% of your days using it. That is about 5000 hours. Say you get 10% speedup using 1.8ghz i7 vs 1.7ghz i5. That saves you about 500 hours of time. 500$ more for 500 hours time back. ;)
I don't think you were being totally serious, but I don't think this justification works (even assuming you got all the hour numbers right) because for the vast majority of the tasks you're going to be doing on the machine (e.g., web browsing, coding, etc.), the speed differential between the i7 and i5 will save you 0 time.
Exactly. I think the grandparent is missing that only in very special circumstances does the i7 make a difference, probably less than 1% of your time.
Lets assume its 10%. 3 years * 52 weeks *40 hours per week= 6,240 hours working.
Lets assume that for 10% of that day you're using your computer in a way that the i7 is able to make faster. Assuming you get 10% speedup, that saves you 62.4 hours, the equivalent of paying yourself $8.01/hr.
But frankly, assuming your computer spends 10% of your workday performing i7 optimized tasks seems high. 1% is more likely (if not still unreasonable). And at that rate, you're paying yourself $80.13 per hour.
And keep in mind that you are paying yourself to sit there for an extra couple microseconds between computer operations.
Not that you shouldn't get the i7. Just don't dream that its somehow paying for itself!
