Color purity of any display device is typically referred to in terms of NTSC Ratio. There are 3 primary colors defined by the NTSC standard. They form a triangle on a CIE chart. When you plot the primary colors of a LCD or other display you get another triangle. The measurement then defines how much of the NTSC Triangle is covered by the triangle of the measured display device.
The dot pitch of any LCD monitor is fixed. It's not going to change or improve for a given panel size/resolution. Every 20" UXGA monitor ever made has the exact same DPI.
There are no 7 bit LCD panels. There are 6 and 8 bit LCD panels. The only difference is in the LCD drivers that are attached to the glass. Response time has nothing to do with the number of bits a panel uses.
6 bit panels use a controller that does dithering. When properly implemented it is nearly impossible to see the difference between a 6 bit panel with dithering and an 8 bit panel. Still, more and more panels are coming with 8 bit drivers.
Response time is never going to make a CRT lover happy. The problem CRT owners have with motion on LCDs has nothing to do with response time. FYI, panels used to be rated black to white to black, but it was discovered that some LCD panel technologies had very good B to W to B time, but poor grey to grey times, so now grey to grey times are all the rage. The motion "problem" with an LCD is that it is not an impulse display like a CRT. It is a motion hold display. Our brains percieve a motion hold display as being blurry when in fact it is not.