Choice for me is i5 - 4G - 128SD refurb for $929.
Or i5 - 8G - 64SD new for $1099.
The idea is that I can never upgrade the ram, but I could the SSD.
Still its a big price difference just to get the 8 and lose the double SSD.
If you have to ask then you don't need more than 4GB of RAM. Anyone who needs more than four gigs of RAM is acutely aware of this and can easily explain why because when the RAM runs out everything stops. I remember back in the day when computers came with 384MB of RAM.
If you're using your Air as a desktop you're overtaxing it and you should not expect a happy ending.