Hi, Don. The POH table is actually pretty accurate, assuming you use the prescribed technique as listed in the Associated Conditions and airspeed tables on the chart.
The POH chart accounts for density altitude by comparing the raw information (pressure altitude and temperature) in the left-most block of the chart. It may help to copy it from the POH and blow it up for easier reading.
You might take AOPA's online Mountain Flying course before your trip west, and even consider a stop along the Front Range to fly with an instructor from the Colorado Pilots Association. One item you'll see recommended frequently is to fly early, in the cool part of the day. Another is to fly as light as possible--the Colorado Pilots Association, for instance, recommends no heavier than 200 pounds below maximum gross weight for your mountain takeoff. If need be, fly out of the mountains, land and refuel to make it al the way home. It's vital that you practice good mixture control for takeoff and climb, and fly the book airspeeds to get "book" performance--the attitude needed to get book speed will be lower at high elevations than what you're used to.
Have a good trip!