If you are trying to benchmark V5 vs. V4, the initial creation time will be pretty comparable. It's when changes come along, however, that V5 will run circles around V4.
That being said, there are some features that V4 does better than V5. There are other features that V5 does better. It all depends upon what you are doing.
In a real design environment you should see about a 15-25% reduction in Solid Modelling time in V5 over V4, mostly due to the constantly moving design targets and V5's ability to change things on the fly. Once you start implementing the more advanced features of V5 such as PowerCopies, User Features, Design Templates, Relational Design, etc. You will start to see significantly more savings.