A few points after reading this thread:
Short high-quality barrel > long cheap barrel.
I would buy a shorter prometheus barrel over a longer barrel by just about any other band.
Buying a long barrel tight-bore, then using .20s defeats the point. If your going for accuracy, use at least .25s. I would aim for .28s probably.
If you want to increase your accuracy, Hop-up rubber should be priority over a new barrel.
Guarder clear+SCS is a winner in my books.
Lastly, I have always really felt long barrels are over-rated. I built my first AEG with one, thinking accuracy was king. Then i played my first game, and realized that the minor accuracy increase was not worth adding this big cumbersome tube on the end of my already long rifle.
It's better to light a candle, than to curse the darkness