Radeon RX 550 @ 128-bit 4gb ddr5 is higher up with a score of 2718, priced at $158.
Radeon 550 @ 64-bit 2gb ddr5 is 2nd from the bottom with a score of 1958, priced at $99.
RX550 = 50watt, Dx 12.0, pcie 3.0 x8, core clock 1100 mhz, memory clock 1750 mhz, opengl 4.5, overall rank = 406
550 = no data, Dx 12 says 14 frames/sec.
Why I feel 4 GB variant can not be a good choice...
the 4gb variant is the better choice between those specific two, as benchmark scores (if u believe them) also point out. The redit rationale about not being able to use all 4gb anyway is ridiculous. If it uses 1mb of video ram or 1000, 128-bit will operate twice as fast as 64-bit, simple as that! Where the rubber meets the road is in the comparisons between clock speeds of everything, which i cannot find for 550. But like with all other graphics cards makes/models the variants are always faster... usually the result of minor overclock, and sometimes extra ram.
The RX550 is better than 550; the 550 will not outperform the rx550.
There are many better cards than RX550.
Radeon RX6400 @ $160 second from top at best value chart: https://www.videocardbenchmark.net/gpu_value.html
the biggest factor may be in 550 not supporting latest versions of openGL and DirectX where the RX550 will, so that reason alone will likely make rx550 better than 550. The "550" probably went obsolete a few months after release when AMD got the rx550 selling, now the "550" is just obsolete already built cards that haven't been recycled yet where sellers are just looking to offload them.
what i could find: https://www.techpowerup.com/gpu-specs/radeon-550.c3407
550 shows same clock speeds as RX, so no, no way it'll ever be better than rx550; all amd probably did was update the memory bus to 128-bit and double the vram circa 2017 to compete with market competition.
and given the fraud in the graphics market, hard to tell 550 from rx550 from 560 and 570; what you find as "rx550" advertised as 128-bit 4gb ddr5 you might get a 64-bit 2gb card so be careful with end of life stuff like that.