It's time for some
Dolphin testing.
First, I went with 4.0.8680, comparing it with the latest official 4.0.2. OGL backend, v-sync, 2,5x internal, no AA, HLE audio.
RE0 &
RE1
There are visible slowdowns during scene transitions. FPS drop to 20-25 frames (same thing happens in 402), but there's visibble chopping, not present in 402, esp. when you reach some are for the 1st time.
Another bad thing is that the Custom Projection Hack has been removed - I've been using it to remove the irritating DoF effect in both games. Emulation accuracy my ass...
Metroid Prime
Newest version runs FMVs at 30FPS (WTF?) but ingame it runs MUCH faster than 402. It looks like the "Shader Compilation Stuttering" is gone - game runs very fast during the entire rendered intro, no heavy hiccups present in 402.
Zelda - TP
Looks and works the same on both verions (full speed, no visible artifacts):
Tested latest Ishiiruka build as well, using DX11 backend and "Full Async Shader Compilation".
Metroid Prime works smoother than in regular build (almost no slowdowns whatsoever).
Ishiiruka builds look more interesting than regular ones due to more options (fixes, hacks, audio & video output quirks).
Problem: sometimes DX11 won't launch properly when "Use fullscreen" is enabled. Affects both latest regular build and Ishiiruka build. Solution: start in window, then alt+enter to fullscreen.
This also fixes the FMV slowdown in Metroid Prime, mentioned above.
Verdict:
Gamecube emulation's level is coming close to the N64 level. At least in amount of fiddling-around required.