I am currently running BigClive RGB Floodlights off of an MR16 with CAT5 as my wire of choice between my components. I am also running 5050 RGB flexstrips off of the 3 Channel DMX controllers. Here are some thoughts:
1.) Watch your amperage. I believe that you can run 1 amp on Cat5. Others smarter than me on this forum can confirm this.
2.) Used Stranded wire for your connections! Solid just breaks too easy!
3.) Monoprice.com is usually the place to buy your pre-made Cat5 cables for a great price.
I like the ease of setup of being able to string Cat5 from my controller to my floods and be done. It is quick, easy, works and the cables are small. I also like the even dimming of the MR16 board, something that can change depending on the 3Channel controller you buy.
I also like the ease of wiring from the MR16. You can take your orange pair and call them red, your blue pair to blue, your green pair to green and your brown pair for common positive! When you are power injecting to the DMX controllers your cabling gets slightly more complicated, not much, but some!
I like having 1 power supply vs. several around the yard. Just saves on 110V wiring!
I actually took my MR16 and a PC power supply and put them in a cheap plastic toolbox that I had laying around. It was easy to add some PVC fittings to the box for cable ingress/egress and ventilation. The whole setup sat outside powered up from the day before Thanksgiving until January 7th! No problems.
Now for the 3 Channel DMX controllers. Those have a place and work well, but they are different! You can use 1 1/4 thing wall (Schedule 120) pvc for housings, you can mount them closer to the item, but you still have close to the same amount of cable in most cases. If you are going to pursue this route, please go to Holidaycoro.com and look at RGB video's that David has posted over there. He explains the controller differences, the RGB packaging differences, cabling, etc. Great Reference!!!
Also, there is a thread elsewhere on this page that discusses an EBAY item which is a clamp on connector for the flex strips! Regardless of how you go with the controller, If you are using the flex strips, I highly suggest looking that these!!! My biggest problem in using the flexstrips was soldering wire to them and not having any breakage! I think these connectors would have helped immensely!
Good luck, have fun, and create something unique!!!
Oh, and by the way! I wouldn't rule out R.J.'s Smart String controllers on flex strips either! You can get more interesting effects using these and they unite the best of all worlds! Cat5, small local controllers, centralized power, and pixel control!
Mike.