Is a Ideal cut much better than a very good cut diamond?

Independent grading labs use different metrics to evaluate the cut. The scale from best to worst is: Ideal (AGS only) Excellent (AGS, GIA) Very Good (Most labs) Good (Most labs) Fair (Most labs) Poor (Most labs) Each grading lab has slightly different criteria, though it is generally accepted that AGS is the most strict followed by GIA then EGL, then any others as less strict (e.g. a "Very Good" from a less strict lab may be graded as a "Good" by a more strict lab). Many companies use the term "ideal" to describe their best diamonds they sell, though they may not actually be independently graded as "Ideal".