I went with RGBW LED strips. They add cool white or warm white LEDs between the RGB LEDs so you can get a pure white. The white created with RGB only isn't very bright or white...

I used this kit on Amazon. Working great. it includes a 5A power supply and controller in each kit - $27 http://www.amazon.com/gp/product/B00KQGLQOC

I also picked up some of these to couple multiple kits together - $10 http://www.amazon.com/gp/product/B0144NLSMW

I used this for extension wires - $7 http://www.amazon.com/gp/product/B00YTEUEEU

These parts have been reliable so far over the 3 months I have been using them

Also, I recommend soldering the connections if you are at all capable. The crimp on connectors for LED strips are typically poor quality and result in an unreliable connection over time. Get some heat shrink tubing (I think I used 1/2") to put over your soldered connections.

Also, do not run the ribbon cable wire over long distances. The small gauge wire used in the ribbon cable will result in a voltage drop if run too far. Put the controller or booster close (within inches, if possible) to the LED strips and run the DC power wires the long distance using 18ga wire or bigger (speaker wire is a cheap source for long runs of 14 - 18 ga wire). Better yet is to also place the power supplies close to the controller and run longer AC power cords to the power supplies.

Only have about 20 feet in total in smaller strips lighting up some cabinetry so I can't really can't comment on longer strip performance. I thought I might need closer to 30 feet so I got the booster. I am running all 20 feet from the booster, not the controller.

If you can, I would run 12V power out to the middle of your beam, put the controller and booster out there and power the strips from the center. You will only have about 10 feet powered which should avoid any voltage drop problems.

The controller I posted and am using will retain the last setting when the power is restored.