A QVW-file with a fully developed application and non-trivial data size always take more space in memory than on disk. The file image is hghly compressed. So an application might easily expand to twice and much more when it is opened. It is hard to give an exact figure due to several factors that determine in-memory compression vs on file compression.
So I would say that 4GB memory for a 4GB QVW-file is impossible or next to impossible. My gut feeling tells me that at least 8GB but maybe even 16 GB of RAM would be necessary to run the app at speed. The Windows itself needs quite a bit of memory to run at normal speeds.
The good news is that if you are in control of the application it is possible to tune an application to use much less memory and become much speedier even without doing much about the number of rows in each table. The important thing is to get rid of unneccessary fields and tuning the cardinality of values for each field (if possible) that has many values (rows). Even splitting fields with high cardinality into multiple fields of much lower cardinality. Timestamps are really often the bad guys that require lots of memory if not rounded off to a precision that is necessary for analysis purposes.
