Yes, there are steam machines available.
Yes, there are steam machines available.
You're focusing on FX options, and it's the least reliable among them despite being budget-friendly. Pairing it with an older chipset might keep it stable, though opinions vary. If you're leaning toward AMD, consider the FM2 alternative.
You're considering a PS4 build at 500W and unsure about saving money. If you can save between 700-800, it would offer a significantly better experience than a console. For 500W you'd likely choose a console. With your setup, having two RAM sticks in dual-channel mode is fine; an i3 or i5 will suffice, and a 8GB memory module could be a good investment for long-term performance. The 280x model is a solid option. If you're planning new builds, you'll get much more processing power. Are there any other savings you're looking for?
Consider upgrading to a better CPU or a clear path for improvement, like an AM4 or Z97. Opt for a slightly weaker GPU, such as 285 or 280, and ensure you have at least a 270x performance boost. Keep an eye on sales and explore other people's budget builds. An Xbox One and PS4 can match an AMD 7850 GPU, but a 280 would handle it well.
I wouldn't revisit /r/mustardrace anymore. Buildapc is a solid alternative, though its design seems decent. It would provide reasonable performance, but I’d suggest checking the local used market first. Purchasing an AM3+ motherboard would tie you into AMD processors that won’t be around much longer. The 6300 chipset is fine, but the 8500 might be better if you're aiming for more flexibility. If you can, save a bit and consider an Intel board with the 3258 chipset instead.