I wont really answer your question, but conceptually speaking, the overall performance is usually better in a star schema data model rather than in a single table. Of course, there are a lot of other things to consider which may be contrary to this recommendation.
I'm attaching the document QlikView Best Practices, from 'Enterprise Framework', and in page 15 you will find a brief overview of data models.
Hope this points you in the right direction.
If you want to use the currency rate for calculations, then this might be a reason to keep all numbers in one table: I assume you want to make a calculation like Sum(Cost*CurrencyRate).
If the two fields Cost and CurrencyRate resides in two different tables, then QlikView will need to generate all possible combinations between two tables before it can start calculations. But if both numbers are in one table, the calculation can be made directly. So I suspect it is better to keep all numbers in one table.
However, to be really sure, there is only one way: You need to test...