Just wanted to post to say I'm very into RA and if anyone is having trouble finding a good filter for GBA then I modified a preset a bit and thought it looked great on a 65" 4K screen, was so hard to get a balance of having the pixel grid but its not being too defined. I don't think its very accurate to what the AGS-101 screen would actually look like but it makes the pixel art look as sharp as possible while also making the sprites [Is that even the right word?] look great.
The oversaturated colours of Metroid Fusion and The Minish Cap I corrected with the core built-in colour correction but I think it desaturates those games too much so I combined a pass of GBA-color with my modified CRT-Caligari [Which includes bilinear filtering I think so you can turn that off in the general options if you have it on].
All the GBA ones I tried were authentic-looking but didn't actually make the art look great at 4K, I'm got the scaling set up pretty well I think but maybe I shouldn't be running GBA games at 2160p to begin with, I do it to get a slightly lowesr input lag on the telly.
Got any pics?