Pascal, 

We have many products each with 3 variant categories, resulting in over 246 variants per product.  Trying to use the filters that are provided barely speeds things up, and in the odoo online version that we are using it is next to impossible to create invoices with 100+ line items consisting of these many product variants.

What i've done on my end is create and internal reference with a "part number" like scheme.  

For your Product AAA with variant category B and C.  

then say 4 of each B and C.  We came up with something like the following and it made making the 100+ line items per sales order process drop from 20 minutes to less than five.

[Internal Reference Field]

AAA-B-1,AAA-B-2,AAA-B-3,AAA-B-4,AAA-C-1,AAA-C-2,AAA-C-3,AAA-C-4

This is similar to how auto parts companies keep track of different components.  The "-" seperates your product, from each of it's variants.

Hope this helps