I feel the picture is somewhat clearer as regards this line of AMD graphics cards. What we seem to have is the 5500 XT as the replacement for the RX 580/590 card, while in my mind the 5600 XT is more akin to the Vega 56 (helpfully they both have "56" in the name). I still feel that it was somewhat odd to have offered a 4 GB version of the 5500 XT - yes, there was a 4 GB 580 card, but why offer the newer cards with this specification?
If I'm honest, I was expecting that this generation of cards would be one where you didn't need to drop settings to Medium to maintain a 60 FPS frame rate (apart from exceptional titles like Metro: Exodus), whereas this review shows that this isn't always possible with the 5500 XT, at least not with a card that is hamstrung by the combination of only 4 GB VRAM and a PCI-e 8.0 interface.
So if the 5500 XT is just about capable of 60 FPS at 1080p Ultra in the majority of titles, is it wiser to buy a slightly more powerful card to ensure you can consistently achieve high frame rates, especially if you have a high refresh rate monitor? The next model up in the AMD range is the 5600 XT, so would the 5600 XT be the better 1080p card, if the price is right?
What makes things more complicated is that it has 2 GB less VRAM than the 5500 XT. If you remember, I likened the the RX 5600 XT to the Vega 56, and it seems to outperform it at 1440p, so the RX 5600 XT (like the GTX 1660) should be fine for high frame rates at 1080p Ultra. This is assuming that only having 6 GB of VRAM doesn't become a performance choke point in the same way that 4 GB currently is on the 5500 XT, but we won't know until such time as it does or doesn't happen.
Other than that, you have to start thinking about whether the GTX 1660 is the better option - either way, I'm not convinced the 5500 XT is the card to buy for 1080p gaming if you're after high frame rates and/or running with the highest settings. I guess my take home message from this is that there may always be a need to overspec your graphics card to achieve the level of performance that we are told we should be looking for - either that, or be prepared to dial back the settings to maintain those high frame rates.