Improve Performance of Power Pivot Model Designer in Excel

[MKuschel]

Actually Excel es getting really slow when working on large models (35 tables in my Case, not much data - only 30 MB). Opening Power Pivot Designer takes several minutes on an i7 machine, adding an Attribute may freeze Excel or be unresponsive about 10-20 minutes. The Designer in Visual Studio is far better, but not available for anyone. Please improve this.