I have tried kmail, Geary, mailspring before I landed on betterbird. I’m not sure what you mean with slow, but it works without issues on my pc. It does a lot of stuff, but it’s a fork of Thunderbird, which you want to exclude based on the initial thread. There are not a lot of linux clients even worth trying. Good luck finding your jam.

I’m using endeavourOS with Nvidia 4090 with proprietary drivers and it works fine for most games without tinkering. For issues with Linux gaming you can check protonDB. Steam, lutris and heroic game launchers are doing wonders for a big portion of the gaming options on Linux. I wouldn’t change the 3080 with AMD if I were you.