So how does the profile help with the colour gamut? Basically a paper profile will try to maximise the gamut of colours that your printer can print. Your printer and paper combinations only have a certain gamut, but your standard printer driver will almost certainly not be using the full gamut - the driver will be on the safe side. With a profile, you should find the gamut gets extended. It might not be by a huge amount, but there will be at the very least a subtle change. There'll probably be more shadow detail, brighter colours, and a better distinction between shades of colours.
• Neutral black and white. Very few printers can print a neutral black and white print - more often than not there are colour tints to the shades of grey, and some shades will show one colour of tint, whilst other shades will show a different colour. This makes it very difficult to correct. However, with a profile your black and white prints should become neutral as the tint is removed individually from each shade of grey. However, please note that a few inks do display a condition called metamerism - this is where colours change under different lighting conditions.