5000 only with 18 cards ? That's low. I easily get 324-330 h/s per card.

That's on different brands as well. I have msi gaming, asus strix and asus dual.
I get that range on msi and strix. But that asus dual card gets me only about 308-312 h/s.
So basically you're not overclocking those cards well. You should get almost about 5900 h/s.

I guess you probably guessed what coin you're going to mine. Since you have nvidia cards just like me, Zcash is your friend.
I've tried mining ether, zclassic, xmr and many other coins. I even used nicehash for two months (and it was the worst profits).

Zcash is the best if you overclock them the way I'm telling you. Its price spikes every now and then and that's when you sell.

If you need help with overclocking I can tell you my settings for each card but tell us what brands those 18 cards are.