These are the parts I have (that are relevant)

Motherboard - http://www.newegg.com/Product/Product.aspx?Item=N82E16813128514 Processor - http://www.newegg.com/Product/Product.aspx?Item=N82E16819113291 Current card is a GTX 550

Looking for something under $300.

A GTX 1050 Ti will only run you about ~$150 . 1060 is probably around $250. While sometimes its' better to up the second digit over the first (the first is version and the second is a performance rating), in this case it doesn't seem like this gets you any gains.

I'm a Radeon fan, and given that the price:performance ratio sucks on Nvidia cards, you're better off with an RX470 or RX480. The 470 is around $159 with 4GBs of GDDR5 and the RX480 is around $200 with 4GBs of GDDR5. What you should be more concerned with is how many Stream Processors you get, with the RX470, you get 2048 SPUs and on the RX480, you get 2304. Obviously the RX480 is the more beefy card, but you'll still get a good gaming experience on the RX470. Where the Radeons excel more than Geforce cards too, is in scaling on Crossfire. While it takes more technical know-how to get multi-GPU systems to work, my 2 R9 290x video cards in crossfire crank out 1440P gaming at 70 FPS or so, depending on the game and level of support for Crossfire. So, if your motherboard supports Crossfire, an easy upgrade would be a second GPU. This does put significantly more stress on your power supply unit, though, so you'd best know what kind of power supply you're using and if it can handle the stress of high TDP draws. My 1000 watt unit works well for this, and handles the 2 300 TDP card, in addition to the Intel Core i5 4690K, 16GBs of RAM, and the 15 or so USB peripherals (most by Razer and Logitech), being used on the system. If you need further advice on this, shoot me a line.

EDIT: Looking at your mobo, it does in fact support Crossfire, so my previous point about the Crossfire support, is valid.

EDIT 2: Looking at your CPU, it's a little underpowered in today's gaming environment, and you might want to consider moving up the Vishera line of AMD processors. The FX-8350 is a nice chip for that board, and they're pretty inexpensive too. If you can afford to buy both the GPU and the CPU, it's a good idea to do so, since bootlenecking is a real possibility on that CPU.