From my experiences, which are mostly in the west, New Mexico has got
to be the best state to speed in. Expecially if you want to go for the
top end. I drive from Las Cruces to Denver a couple times each
semester and have cut the drive down to 7hrs (usually 10-12 depending
on how slow you go) but most of the time it takes about 8 1/2 hrs. The
places to watch it are I25 from Las Cruces to North of Alb. There is a
shorter and quicker route east of I25
  Colorado isn’t too bad but they do occasionally use the airplane bit
and I got nailed by vascar last time down (81 in a 65  <sigh> and $69)
  Missouri is also a good place to speed,expecailly if you have a
detector.
   Kansas is good in the rural areas but on 70 it can get
hazardous to speeders.
   Basically in all the states out here if you stick to the two-lanes
and the back ways you may get a bumpier ride but you will save on time!