Jason,
This might give you some insight into quantifying good optics.
http://www.rfroyce.com/standards.htm
The current best (single) scientific criterion is the measure of the Strehl ratio of the optics, it is a measure of how well the scope is able to take all the light (energy) coming into it and focus this into the (first order) airey disc.
The ratio is a function of what the scope can achieve compared to the theoretical maximum that is possible.
The article attempts to explain it and also to correlate that back to the traditional 1/4wave to 1/10 wave optics style of measurement that most people are familiar with.
Any optical imperfections and aberrations, whatever they are, will affect and reduce the Strehl ratio, but stated simply you just can't get a high number unless the optics are very good.
Of course there is more to it than only this, but generally if the Strehl ratio is above 95 then you have a very good scope, greater than 99% and its near perfect.
This is vastly different to a statement that a scope is "diffraction limited" - whilst not totally meaningless, it says almost nothing really about the real quality of the scopes optics.
You might be horrified if you knew what the numbers are for a lot of scopes purporting to be very good by hiding behind meaningless waffle.
The sooner all scope manufacturers start putting useful numbers (like strehl ratio) behind their advertising the better - as it stands now many buyers are being mislead by the omission of this sort of information.
Hope that helps
Regards Rally
PS Another useful measure for assessment (especially for refractors) is looking at the ray fan plots of coloured light to see how well they focus - as a measure of the degree of chromatic aberration. Some are extremely well corrected, most are not. But you will pay substantially more for those that are corrected.
Once again getting this info is difficult if not impossible.