Epson's printer driver limits page length on the 3880 to about 37". Some third party drivers (including some software RIPs) bypass this limitation. Hence the suggestion to get RIP software in order to print panoramas.
The 3880 hardware is not designed to handle long sheets. If you are printing on long sheets you need to pay attention to proper paper feeding of the sheet into and out of the printer. If the long sheet was cut from a roll, you need to remove the curl from the sheet. The 3880 was not designed for curly paper.
The 4880 and 4900 are designed for roll paper, and do not have these issues.
On the other hand, the 4880 and 4900 have a minimum paper size of 8x10 inches. If you want to print on smaller cut sheets (5x7, 4x6) the 4880 or 4900 may not be good choices.
I like that I can put a stack of paper (including odd sizes like greeting cards, or 4x6 proofs) and let my 3880 print away without me having to babysit it.
The 3880 and the 4880 have identical print quality. The 4900 offers slightly better gamut.
Ink for the 4xxx printers cost less than ink for the 3880.
The 3880 is a great cut sheet printer for sizes from 3.5 x5 up to 17 by 25 (note: Epson's driver supports borderless on 17x22, but not on 17x25). Epson's design limit for the 3880 is about 17 by 37".
You can get a 3880 to print on paper longer than 37", but this is not something the printer is particularly good at.
The 4xxx series printers can print on cut sheets larger than 8x10, and very long prints on rolls. The minimum paper width is 8".
I may be wrong, but my understanding is that the 4xxx series will not print borderless on cut sheets. If you want borderless prints you must use roll paper.
The 4xxx series printers are much larger than the 3880 printer.
Both are good printers. Pick the one that is a better match for your needs.