You are go for any ASIC miner like antminer l3+ or S9. These will be give the better profit than you are finding in the GPU rig you are making now. Please let me know that you gonna make how many number of hardware in your farm. I think with the 4k USD you can find the 2 hardwares in ordering it on bitmain site.
But other resellers in Ebay or other sites you will get the miner but the rate will be more than expected you find in the bitmain site. That is major probleim. Since already involved in mining you may know reseller so check with them for antminer s9 hardware to make more money.
Thanks for the input bro. i checked the nicehash Profit calculator and saw antminer is about 10$ behind baikal in terms of Profit/day. not to mention, Baikal will be adding 2 Algos for a much better profit potential in the future. Would you still go with Antminer instead of Baikal?