Anderson: yeah there’s something wrong with the newest cores, trying to launch naomi games makes RA crash hard. I went back to an older version.
Awakened: yeah I’m using regular reicast, oit is much, much heavier. Hard sync frames are set to 1 too, much more fluid that way, and that extra frame of input lag is something I can live with.
kondorito/legolas: thanks, it actually looks much better in motion, fullscreen : )
Regarding the shaders, my configuration is highly optimized for my tastes and the limitations of my old machine, but I will try to explain. See, in my experience, RA native crt shaders don’t go well with high internal resolutions, the scanlines are displayed wrong or they simply disappear. So for cores that allow them (reicast, beetle psx hw, desmume, mupen64, ppsspp, dolphin…) I go with a mix of retroarch + reshade. Without reshade, I don’t know how to get proper scanlines at high IRs. As for the rest, crt-easymode-halation is my favourite shader for LDTV (240p and similar) content. But that’s a story for another day : )
On reshade, crt-hyllian (which was skillfully ported from RA to RS by a good man that calls himself Matsilagi) + some gaussianbloom. On retroarch, aa-shader-4.0-level2-pass2 (with a very high offset for dreamcast, around 0.75, which makes everything nice and smooth while keeping fine detail and textures alive) + image-adjustment for saturation, gamma, levels etc. Oh and linear filtering of course. At high resolutions, everything looks overly sharp and dry without it, specially 2D graphics.
Screen res is 720p (these old games don’t really need more than that, it’s a nice integer multiple of 240p and it helps keep performance high and temperatures low); internal res is 1280x960. Aspect ratio is 1.36 (4:3 being 1.33, I think a bit of a horizontal stretch goes well with many dreamcast games).
Everything looks fantastic scaled up with different combinations of reshade + retroarch shaders (which depend on the system’s original video output), from mario 64 to ffvii (and its dreaded lo-res pre-rendered backgrounds) or of course, soul calibur. Aaah, what I could do with one of those beefy computers that you guys have! : )
I’m posting soul calibur examples only because it’s what I have at hand at the moment, but if you want to see more screenshots from other games or systems, let me know. The artifacts you see in the images are due to lazy jpeg compression. They will not be there in-game (or in png captures).
And amazingly, I just checked and with these settings, soul calibur runs at 60fps with a cpu load of 5-12% @ 2295Mhz while gpu load never goes past 50% @ 580Mhz. Cool, and quiet 
It might be a bit overwhelming for the casual player, but Retroarch is the best thing that happened to emulation in general in a long time, heaven on earth for obsessive tweakers like myself. And the people developing it and the cores, a troop of angels.