The 66 & 88 have the same appearance, in my testing. A tech at RR told me that the inkable surface of the two papers is identical, such that any custom profile made for the 66lb will look the same on the 88. Near as I can tell, it's probably true. The 88 does feel better in hand, but it's still not really a substantial paper in that sense.
I print a good bit on metallics, and have wound up working with the Breathing Color Vibrance Metallic, in roll form, most of the time. So I can't offer too much more on the Red River metallics.