I came with the forecast calculation after long time mining and validating weekly during this time with Whatomine, coinwarz and mycryptobudd

I invested in a GPU rig that costed me $3500 (3x1080’s) OR I INVESTED about 7ZEC OR  0.23BTC at the time that I got into.
Observed 15% monthly difficulty change since I started and I got -15% less coins per month (matches) then I used forecast with 15% difficulty change and got 4ZEC in 18months
$50/month electricity about $1000 in 18months

http://www.mycryptobuddy.com/ZCashMiningCalculator


I did a “What if” scenario buying  6 more 1080’s at $900 each (taxes etc) = $6000
3500 + 6000 = $9500 total investment, total cost 7ZEC + 14ZEC (at march 18) = 21ZEC or 0.8BTC
9 cards = 5220sol/sec, in 18months will produce 11ZEC at 15% difficulty change, if is more then even worst
Then AT THE END OF 2020 I might get my 21ZEC back.

Monero mining: same results (but I never assembled in Dec2017)
Rig after 3 months later and in the middle of the crypto drama:
the difficulty is X3 (WOULD BE MORE IF MARKET WOULDN'T CRASH)
using the same parameters the calculator (best calculator out there) month by month at the difficultly of those periods today I would have 8 XMR today

price of XMR is the same at that day
my investment would be $7000/200=35 XMR + electricity ($400 in 3 months) + MY TIME THAT IS VERY EXPENSIVE
then I would need at today (35-8=27XMR) to recover the investment.

In the best case if difficultly remain the same ( a dream) then the calculator shows 18months to make 27XMR + $2400 in electricity and I am 2 years older... with heat and noise and technical issues that i solved for sure.

Investment $7000+400+2400 = about $10,000 (same that the ZEC dedicated rig)
In 2020 I would have the same 35XMR that Invested in Dec2017.
then if I would invest $7000 and get 35XMR in dec2017 then you CAN MAKE YOUR CONCLUSION FOR YOUR SELF BY CLOSING YOUR EYES AND IMAGINE HOW THE YEAR  2020 WILL BE IN THIS REGARD IF YOU HODL INSTEAD 35XMR.

WHAT HAPPENED IN THIS SCENARIO (along 2018 to 2020) IF HALONG MINING OR OTHERS COMES SUCCESSFULLY WITH THE ASCI AND MONERO CANNOT STOP IT?

MAKES SENSE THE COMMENTS THAT MORE COINS ASIC RESISTANT WILL COME WITH GOOD PROFITS, BUT ZEC WAS VERY PROFITABLE IN JULY 2017 AND JAN 2018 THE REST WAS AVERAGE, NOW IS THIS $3500 RIG IS MAKING $3/DAY AND I STARTED AT $20/DAY

DOES THIS SOUNDS LIKE A MESSAGE FROM THE FUTURE?

IS GPU MINING A GOOD INVESTMENT?

Please let me know comments based in expertise

thanks a lot