Re: (XMR) Monero mining with 4x RX 560 4GB

So I'm thinking of cashing in some of my BTC, to the tune of $900 and buying 4x RX 560 4GB cards to mine Monero, or even possibly Ethereum (or ethereum classic depending on whichever is a better investment...) Each card should get a base hash rate of 350h/s.
Mining calc tells me that it's $80, with current difficulty and price, a month, on the cards alone (mining Monero).
So is it a good idea to buy them and try my luck with gpu mining or keep the bitcoin and hope the price keeps going up?

You forget about one very important information when you asked your question ...
How much are you paying for electricity (with all the taxes) ? this is a mayor factor to calculate your mining income.

with current difficulty , monero/fiat exchange rate with 4 cards you can get around 80$/months minus electricity
if you have to pay 9-10 cents/kwh (or 0.09-0.1USD/kwh) you not going to make any extra income with current difficulty and monero/fiat exchange rate as of today 09/23/2017 .. what you mining you going to spend on your power bill Sad

use a very simple mining calculator , put there your electricity rate and find out ...
Coinwarz Monero Mining Calculator

I'm paying $0.06/kwh for my electricity, which works, but I'm wondering if I will get ROI back, and if I should even buy the miners.
Should I mine for the 4 months and hope that difficulty doesn't hike or just keep the money in BTC?

450mhs is optimistic - you need to have the right cards and the right bios/settings to reach that. Out of the box they do 315-330.

Even if you get 450mhs, it's going to take you 8-9 months to break even on the cards. If you're going into this for short-term (one-year) profits, it's probably not going to work for you well. If you're doing this as a hobby, and you like tinkering, and you plan to mine and sell a portion of your mined coins to diversify your altcoin portfolio to hold for the long-term, then it might be fun and possibly profitable.