Are you me? haha I was also interested in getting a Powercolor Red Dragon 6800XT, but then I researched a bit and read that Powercolor is somewhat of a second-tier GPU maker, so I'm going to go for a Sapphire Nitro+ 7800XT (not the same price, but only a little more expensive, 540 vs 605 -different markets-).
I have a Meshify C as well, and the Nitro+ is 320mm long while on Fractal's website they list 315mm as maximum GPU length with the bottom front fan installed. To solve the problem of having a 320mm card with a front fan I researched a bit and found out that there are slim fans, so I will get a Arctic P14 slim wich is 16mm deep (compared to 25mm standard fans), and things should fit like a glove (telling you this in case you also go for a longer card)