It's easy to make an assumption that primary inks increase gamut, but it's a little more complex than that. One reality is you can increase gamut in colors that really aren't important.
I've used or still use a canon 5000,6100, epson 3800, 9800 and 11880. Personally I believe the 3800 has better output than the 5000 and the 9800. Output of the 6100 and 3800 are very close, and it will depend on image type and needed color gamut. Most likely you will have areas in prints that are better on each printer, with neither being obviously superior. Thus it comes down to features, such as mk/pk switching, paper handling (roll?), etc. In my case, I would give the edge to the 6100 (the 5100 should produce identical output), but the difference is so slight it takes side by side images of the right type with some very close scrutiny to see differences.
However, you asked about the 5000, and here I believe there is a difference. When using the 5000 you may have problems with grain in some regions (that's why I quit using it), as well as metamerism and gloss differential. I felt the black improvement by canon as well as the screening improvements in the newer canon x100 printer series are pretty significant. The ability for the printer to calibrate itself and maintain a baseline is extremely valuable as well to account for the drift as nozzles clog and are remapped, keeping profiles more accurate over time. Calibration also makes it possible to get better profiles from 3rd parties such as paper manufacturers.
Don't misunderstand .. the 5000 can produce great prints, but if final print quality is your main consideration, the extra cost of the 5100, or a 3800 would be a better choice IMO.