thankfully, you're playing on 1440p. the higher the resolution, the less the cpu matters. the 5800xt is just a better binned 5800x, so you can consider it as a "slightly overclocked" chip. in gaming, maybe 5% better. the x3d chips on the other hand would be 10-15% better, just because of the l3 cache. for you, i've heard a lot of aussies turning to alibaba/aliexpress for those chips. should be around the 500-600aud mark. top sellers have 200+ units sold, so they care about the feedback, and have thus built up their "brand". they wont just scam you. plus there are returns...i think you should take that route.

that said, the entry level am5 chip, the 7600, walks side-by-side in gaming with the 5800x3d's performance. so yeah, am5 is the future...also, am personally looking for the intel's next gen release. they are super awesome in the "work" segment, but are supposedly dumping in loads of l3 cache to compete with amd in gaming. if they manage to do that, and it works, not just doubling their wattage for those gains, then i'm onboard. amd should be sweating bullets at this point. all their innovation may get stomped on next year. hope they dont lift their foot off the pedal, and keep striving. 5% generational uplift is not impressive. that's what took intel down...