You should NOT be buying more mining gear to mine now. WHY? Here's my argument.
Lets do some rough realistic calculations for those who are lazy...
50,000 USD to spend
That will allow us to buy 33 units of r9 390 Rigs that hashes 100MH/s
Compared to 7058.8 ETH @ 8.5USD
We have until early next year to mine ETH. With 1400ETH earned a month with 33 rigs this month, you are expecting about 5 month worth of mining to be able to mine the ETH required to get the same amount of ETH you could have bought.
However, in 5 month's time, the amount of ETH you earn drops by 30% a month
980 in May
686 in June
480.2 in July and so on
That would mean you would need a significantly longer period of mining to mine the same 7058 ETH you could have bought using cash. (not including yourself playing the market selling at peaks and buying on dips which would net you EVEN MORE ETH)
Realistically, By July you'd only have 3546.2 ETH with that 33 rigs. It will take another 8 months(Making that March 2017) for you to get the remaining ETH to hit the target 7058.8 ETH.
Especially if the prices go up, that would make it even harder to realize as more miners will jump in making mining even less profitable.
That said, should the current price of ETH drop below 8.5USD, Buying ETH outright would be an even better option with that 50,000USD you're about to spend on mining. Lets say ETH hits 6 USD/ETH you could just outright buy 8333.33 ETH. That amount is IMPOSSIBLE to mine with the same equivalent value of mining gear you would buy with 50,000USD by the time Ethereum moves to PoS
REMEMBER that this disregards the cost for electricity which would cut 1/4 of your ETH profits at the current state. Which means even at the current state, you would be better off buying ETH itself than to invest in mining gear.
Also that currently as a new miner you would have barely any ETH of significant value to net you a good profit if you trade it at an exchange during dips and pumps. While if you outright bought 7058 ETH, at this price, or lower, a simple 15% ETH to BTC price rise would net you 1058.7ETH!!!!. Being in the ETH Poloniex trading forum for a while now, 15% in ETH price rise/drop is NORMAL. You see that almost EVERY WEEK. Imagine making 15%(1058.7ETH) PER WEEK Hell that's way better than what any miner could net you.
Also as calculation goes, the first rise and fall you catch nets you 1058.7 ETH, the SECOND week, you have 8117.5ETH, another 15% rise and fall and you caught it, will net you 1217.6ETH! it grows more every time.
So, I think I've given a very valid argument here. Anyone who tries to tell you not to Buy ETH and Buy Mining gear is only set out to try and cut his losses and sell his own mining gear during this high season just so he can do what I just mentioned and get himself some CHEAP ETH.
If my calculations are wrong, please correct me. Thanks.
(If you don't know how to calculate and profit from pumps and dumps, you should learn because as a miner you will be trading ETH on an exchange whether you want to or not or else you WILL lose large money by selling wrongly)