По вопросу о виртуальном измерениии
BOLAdding a virtual dimension to a cube does not increase the cube's size because a virtual dimension, unlike a regular or parent-child dimension, does not have aggregation data. Virtual dimensions do not affect cube processing time because they are calculated in memory when needed. However, queries that use virtual dimensions can be slower than queries that use regular or parent-child dimensions.

Т.е. если я правильно транслировал то места жрет меньше, но на запросы может отвечать дольше.
Выводы делай сам...