Hi Darren,
You are on the right track. My set goes 5,7,9,11 16, 20, 28. Add a 2X Barlow and there is not a lot left to fill in the magnification stakes.
For more education on eyepieces I suggest you join Cloudy Nights in the US and cruise the forums there. No offence here to any one, as someone once said .."you just can't shut them up on Cloudy Nights" I know a lot of IISers are on CN. Have a look at this thread.
http://www.cloudynights.com/ubbthrea.../o/all/fpart/1
Before you spend on eyepieces you need to know what is out there IMO.
It's a learning curve for sure.
As the thread says all sorts of things come into play...not just the eyepiece.... For what it's worth I eventually settled on the Explore Scientific eyepieces along with some GSO plossls.... after owning some very expensive ones too. I know this is a lot to digest for a beginner, assuming you are?
Hope this is of some help and not confusing.
Matt