Even more so than a tall but stiff gantry is the problem of finding long enough cutters to reach into the deep molds. Chatter and run-out is a major part of this problem as well.
Most solutions end up with slicing the mold CAD drawings into manageable layers and use various methods of pinning the layers together to keep them properly aligned while gluing the separately machined layers together to form the complete mold.
I have used 6" thick molds made of Renshape 440 that were full of chatter damage and had to be reworked with automotive body putty in order to get any use out of them. These were for aircraft wind tunnel models that needed a high degree of accuracy. These molds were cut on a 5' x 10' ShopBot that had a large Colombo spindle on it.
My point is that the necessity of a very stiff machine is only part of the issue for getting a quality surface finish on the molds. The deeper the mold, the more problems you will encounter.
CarveOne
CarveOne
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