Welcome to Piezography, I am happy to help you get set up and happily printing!
1) The 3800 and 3880 use the same curves. The variety of 3800 and 3880 glossy curves downloaded from our forum are custom curves made for different customers over the years, which we have checked and feel to be good for others to use. These curves are names with the printer model, ink tone and paper, whereas standard K7 curves only list the paper (K7 indicated seven ink shades, and 2880 indicates 2880dpi resolution).
2) yes, both GO curves are identical. I checked the download files, and believe you probably got some MPS curves and one GO curve from our Piezography website, and other glossy curves with the second GO curve from our forum articles page.
3) Again about downloading glossy curves from two sources, the "3800-3880-MPS-EPexFiber" curve is the same (just with a slightly different name, to indicate it works with both printer models) as the "3800-MPS-EPexFiber" curve. The third "WN-SEL-NU" was made for a customer using a custom split-tone system using three K7 ink tones. Both curves are very similar, though differ slightly due to slight differences in printer and inks (and possibly paper as well). I have attached an image showing the two different curves for you to see.
"MPS" curves were made for either Selenium or Warm-Neutral inks (which were originally the only glossy K7 ink tones), but now all K7 ink tones are glossy compatible.
4) Similar to 3 above, yes- both curves are for the same paper, but one was made for a customer using Carbon inks, and the other was made for a customer using Selenium inks. I except the SEL curve to work best with your Warm-Neutral inks.
5) We don't have pre-made curves for Epson's Hot Press or Cold Press papers, but I have attached custom curves I've made for customers using the 3800/3880 and these papers. You can also try the curve for HANptoRag or CANragPto, they might give good results on the Hot/Cold Press papers.
I hope this helps. Please let me know if you have further questions of there's anything else I can help you with.
Best regards and happy printing~ Dana
3880-SEL-EPcoldPressNat.quad.zip (2.79 KB)3880-SEL-EPhotPressNat.quad.zip (2.8 KB)