If you want "Like a real GameCube", then that means 1x internal resolution (IR), no graphical enhancements at all, and it'll generally look awful. If you're okay with that, pretty much any modern intel processor graphics.
However, Almost any low end nvidia or AMD GPU will let you play at 3-4x (1080p) with zero slow down. It's very nice. That build that Piccolo linked will run everything at full speed, at pretty much any IR up to a little over 1080p, with lots of graphical enhancements enabled.
However, Almost any low end nvidia or AMD GPU will let you play at 3-4x (1080p) with zero slow down. It's very nice. That build that Piccolo linked will run everything at full speed, at pretty much any IR up to a little over 1080p, with lots of graphical enhancements enabled.