GPU opinions?

[Daytona Beach]

So after a few months I decided to build a gaming PC as I sold my last one before I moved to Georgia. I was running a 3.9ghz processor with 4gb of ram and a Nvidia GeForce (maybe) 630 2gb card my grandpa bought me like 5 years ago. Everything ran fine back then, Minecraft, GTA IV, etc. (the older games anyhow). But now I have a little bit more stable computer so I'm not sure what card to buy for the computer. I had my eye on an XFX R7 Radeon 4gb card but I am not sure if my local stores carry it. I'm just trying to get opinion on which card I should buy for my setup, I either want the R7 or the MSI Radeon RX 550 4gb.
Here is the MSI Radeon RX 550
https://www.newegg.com/Product/Product.aspx?Item=N82E16814137136

Here is the XFX R7 Radeon
XFX Core Edition AMD Radeon R7 240 4GB DDR3 PCI Express 3.0 Graphics Card Black R7-240A-4NFR - Best Buy

If anyone has any other opinions on cards feel free to let me know, I want to have a smooth gaming experience with little to no lag.
Also, my specs for my computer right now are below.

OS: Windows 10 Pro 64-bit
CPU: Intel Core 2 Duo E8400 @ 3.00GHz
RAM: 6.00GB Dual-Channel DDR2
Motherboard: Intel Corp DQ35JO
GPU: 256mb Nvidia GeForce 8500 GT (this is a very old card hense the upgrade)
Storage: 465GB Hitachi

Minus the card being a 256mb, it still runs quite the few games without lag around 60-70 FPS. Also runs 1440p videos without lag. And don't worry about the RAM being DDR2, I'll be upgrading that to DDR3 along with the graphics card tomorrow.

 

[PP Mguire]

Anything you put on that machine is going to be CPU bottlenecked.

 

[Daytona Beach]

Sorry it took so long to reply, hard drive crashed, computer kept freezing, and had to reinstall Windows. It's been running fine with the graphics card I picked up. I got a new motherboard and CPU on the way. I picked up the Nvidia GeForce GT 1030 2gb from best buy. I also ordered the AMD Athlon X4 860k quad-core processor and the ASRock FM2A68M-HD ATX motherboard and some DDR3 RAM. So I won't have to worry about those parts anymore, just the CPU cooler which I'm switching over to LC if possible, and the hard drive which I will also be upgrading this saturday.

 

[PP Mguire]

You buy those new? Kind of a bad idea considering a Pentium G4560 would run circles around it.

 

[Daytona Beach]

Yes I do, and considering the Pentium is around the Athlon price I might consider buying the Pentium. Never really branched out from AMD processors besides the Intel Duo.

 

[PP Mguire]

Well if you're going to get one do it now as Intel are phasing them out because they're taking too much market share from the i3. They're that good.

 

[Daytona Beach]

Hopefully they're still up Friday for the same price. Just gotta find a decent price mobo.