How far have ss amps really come in the last twenty years?

I have owned and enjoyed my Jeff Rowland model 8 ( recently modded and upgraded by Jeff to the last version) for many years. I recently had the opportunity of comparing it ( after mods) to a few of the current ss models from Gamut, D'Agostino, YBA, Parasound, Sim audio, CH precision, Constellation,PS audio,Pass Labs  and Musical Fidelity. The results were very interesting, because to my ears and in the systems that we did the comparison, the Rowland held its own against all but the most expensive D'Ag and CH amps. Even those were only very slightly outclassing the Rowland in the areas of top end resolution...and a tad in the bottom end resolution. Now the thing is that the last revision to the Rowland 8 was designed by Jeff over ten years ago! 
So, my question for those more technically inclined than myself is...how far has the design of ss amps come in the last ten...or even twenty years?