Refreshing to have some fact based work to look at make it refreshing.

I've used your numbers to redo your calculations slightly differently:

Firstly I assume we invest BTC to generate a BTC profit .

This is as opposed to measuring a USD profit.  The idea being to make the returns a little less sensitive to the exchange rate increasing.

I assumed the $418 spent on the miner was converted to 1.33 BTC (using the 315.17 USD/BTC rate you have in the CSV).
I convert the electricity cost to BTC using the daily rate.  
Total BTC generated = 5.07
Total electricity is BTC1.53
Net income = BTC3.53

So 1.33 turns into 3.53 BTC for a gain of 2.66.

This is still sensitive to price of BTC.

Assume flat prices at 315 USD/BTC

To get an idea what the sensitivity of this income was I set it to a flat 315 exchnage rate. This assume a flat exchange rate throughout the period in question.
1.33 then turns into 3.24 giving a 2.45 gain

Assume flat prices at 1000 USD/BTC
0.42 BTC then turns into 4.5 BTC for a gain of 10.76 times.