The Canon iPF 8300 is one of the more advanced large-format, commercial printers available on the market today. It is indeed designed to produce the highest quality large format prints possible. The key thing about the 8300 is that it uses Lucia EX ink, which is a very new pigment ink formulation specifically designed to produce a wide gamut on print. Similar to Epson's Ultrachrome HDR ink, the solid color gamut reproducible by Lucia EX supports over 90% of the Pantone Solid Color matching system on supported paper types. The Epson 7900 and 9900 are Epson's counterparts, and offer up to 98% Pantone on a specific paper type and at maximum DPI.
Ink is the primary factor that affects print output, quality, and gamut. If you intend to create prints that most accurately reproduce color and render fine tonal gradients smoothly, I highly recommend a Canon printer that supports Lucia EX ink, or an Epson printer that supports Ultrachrome HDR ink. For the widest gamut possible on a variety of unique paper types, such as metallic, you might want to look at the Epson Stylus Pro WT7900. This printer uses a new white ink, part of the Ultrachrome HDR + White ink set, which allows more control over highlight tones and possibly even white point. When it comes to HP printers, they are currently not as competitive in the area of ink as Canon and Epson are. Their Vivera pigment ink seems to date back to 2006, which is pretty old by current standards. Canon Lucia EX was released in March 2010, and Epson Ultrachrome HDR was released late 2009, so these brands have a considerable edge over the competition when it comes to accurate color reproduction.
As for which paper type is best...thats a much more subjective area. Both Canon and Epson wide-gamut, large format printers only support their maximum gamuts on a small range of their own brand of papers. A wide gamut is still supported for other papers, including off-brand papers, however they can't guarantee 90% Pantone Solid Color coverage on every paper type (at least, not yet.)
There are several key factors in choosing a paper for your prints. Not every type of photography looks the same on any type of paper, so you need to choose paper types that compliment the type of photography you are printing. Some types look best on glossy or luster papers, some require bright white or pure white, other types look best on natural papers with warmer white points. Some experimentation will be necessary to identify which paper types, finishes, and white points best compliment the type of photography you are printing. In this area, Epson offers more brand name papers than others, however their papers are not necessarily the best, either. Canon offers a fairly broad range of paper, however much of it is manufactured by Hahnemuhle. There are also plenty of third party papers from manufacturers who have been in the business for hundreds of years, including Hahnemuhle (and Harman), Moab, Museo, Ilford, Breathing Color, etc.
Certain factors of a paper affect the reproducible gmaut when printed on. One of the primary factors that affects gamut is the white point and white brightness of the paper. A "purer" white, one that falls around 5500K-6500K, will expand the reproducible gamut as well as maximum tonal range, as it is a purer, more "white" white. Cooler whites (that show up almost blue) or warmer whites (that show up with more orange or red) will reduce or shift the reproducible gamut, as the paper itself will affect color reproduction. Black and white prints tend to look best with a pure white paper, unless you want the artistic or warming effect of a "natural" white paper (which is what most matte fine art papers provide). The brighter the paper, the greater the tonal range is likely to be. Some papers include optical brighteners, which use UV sensitive material that absorbs UV light and emits light in visible wavelengths. Gloss, semigloss, luster papers often have optical brighteners, which can help improve gamut and tonal range...however since they have UV reactive components, they often require a specific kind of lighting to reproduce color correctly.
Another aspect of print quality is paper texture. Not all paper is equal in this regard, and there are a variety of materials, including wood, cotton, bamboo, sugar cane fibers, used to create the printable surface of a paper. Certain fiber types bring out the most in certain types of photography, and certain textures can help add a bit of artistic flare.
In my personal experience, I've found that gloss or luster papers are best paired with portraits, pure white papers are ideal for black and white prints, and photo rag (cotton) papers with a natural white produce superb landscape prints. I personally try to avoid papers with optical brighteners, however such papers may serve your specific type of photography well, so I would experiment.