Lol, well, I'm definitely not opposed to making another spreadsheet!
There'll always be some variance but if you take a fixed price of BTC and other coins in alts to use as an average then it will make it easier. I usually use a bit more of a conservative amount (like worse case scenario planning) but to rake in $600 per month with your current system only bodes well when things start really going up... alright, time to bust a spreadsheet out once I've done my power up post