On a scale from 1 - 10 how much better is Full HD tv compared to HD Ready tv ?

That depends as a TV can be "HD Ready" whilst only having a maximum resolution of 480i, but it could also be 480p, 720i, or 720p, or even 1080i. Full HD is 1080p (p for progressive scan), which is a minimum of 1920 x 1080 pixels with every line rendered. 1080i (interlaced) is only every other horizontal line rendered, with the spaces in between being black lines. This is actually almost unnoticeable, though on paper it still means 1080p is twice as good as 1080i.

In "real world" application though, the difference between, say, the early "HD Ready" of just 480p is the difference between looking through "morning eyes" where the world seems hazy, and looking around when you're wide awake.

In my expierence 1080p is the best for HD resolution.