Although often the 6 ms ones aren't full color--they're ~232,000 dithered up to 16.2 million. Usually the 20s and 24s (at least the higher end ones) are full color and high refresh rate. But you won't get that combo below the premium, large widescreens. You can usually tell, because the number of colors lists >16 million or 16.2 million, rather than 16.7 million.
As for pushing frame rate? I'm pretty casual, and I'll take a little bit of hesitation in favor of the pretty. OTOH, I don't have any problem with either in most games I have (other than Oblivion).
