Looking only at the gamut issue, you would need to be printing on very wide gamut media to really see a significant difference in your large prints.
When going from a 9880 to an 8300 with my mainly canvas prints, I noticed some modest gains in the blue, magenta, violet area, but nothing overwhelmingly dramatic. However, on wide gamut glossy papers and canvases the 8300 is clearly superior...provided I have post processed the images to take advantage of the wider available gamut.
So for rather limited gamut media like canvas and many matte papers, going to a wide gamut printer will bring modest gains that might not jump out with side by side print comparisons. For wide gamut media expect big gains, but only if you push the envelope with your post processing. For instance, if you have images that you soft proofed for a moderate gamut printer and media, you might have to go back to proofing to realize the image's full potential with a wider gamut printer and media.