How to identify when to move all or part of the data from Sybase ASE to Sybase IQ?

Is there an easy way that any of you guys use to determine this? Ok, we have more than x gb of data, we should go for IQ! Ok, we have more than x reports going, we should go for IQ! Ok, we have a lot of data archived and need better timings retrieving it, we should go to IQ! What are the factors that you use to make this decision?