First off, do you need the layer to be cached? In a web-adf application built in ArcGIS Server (AGS) v10.0, I needed cached layers for the web app to have decent performance. When my organization migrated the web app to javascript/HTML5 with AGS v10.2, the dynamic mapservices were much faster than in AGS v10.0, so the cached layers were not needed. Might this be the case with your setup?
What version of AGS do you have?