There are people who've mixed (I'm not one of them) and there are people who run straight coco (I'm not one of them) to great results. Most important is understanding the medium you're working with, Sunshine Mix and straight coco I *believe* do behave differently and have slightly different requirements, specifically with regard to pH and Ca/Mg uptake.
Yep ran 5g buckets with straight coco last year....the answer was it created beasts that were drinking 1-2g a day!!! I went to smart pots, but the 5g's produced some very nice LARGE ladies.
I grow with coco only in smartpots that I hand water. Ive tried many other mediums in the hydro/soilless arena, and plain coco is the easiest and best that I have used. Water retention, speed of growth and huge yield are all benefits of coco only in smartpots. I agree with SeaMaiden about the differences in ph and cal-mag needs for the mix your trying to run. While I know that a lot of people use coco mixes, I can tell you that coco alone is the way to go. With 30-40% porosity depending upon the brand you use, theres no need for perlite. I run 15,20, 25, and 30 gal smpots depending upon the size of the plant. 5 gals will work fine though. The only thing that I do to plain coco is put a small layer of diatomaceous earth on top to kill gnats and also act as a thermal insulator to keep my roots a steady temp through day and night cycles. I hope that helps.
I ran a coco, sunshine organic mix. Worked GREAT! for first few times. Just watered a few times with pureblend and ended up with some nice yields. Then I saw what was possible. Been using straight coco since. Have run up to 7 gal grow bags. Worked fine. Unfortunately it was a temp setup so not ideal in the slightest to compare fairly to other systems. Yield still killed the waterfarms that I ran before.