Use the mart reporting.
For the source mart, use a data browser report or Crystal report in r7. Or a Crystal report in r8.
For the destination mart, use a Report Designer report or a Crystal report that matches the report in r7 or r8.
Export the reports to another format like MS Excel (CSV).
Then compare side-by-side (eyeball).
Or use a file comparison utility of your choice to quickly highlight any differences.
NOTE: in versions prior to r9.6.0 inherited data was not stored in the marts for efficiency purposes, and that means physical data was not stored in the mart. So the mart reports in versions prior to r9.6.0 will not report on the physical data. To validate the physical data in versions of the mart prior to r9.6.0, you can use the ERwin reports (not the mart reports): use the older version of ERwin (r7 or r8) to open the old model from the old mart, do an ERwin report, open the upgraded model from the r9 mart using r9 ERwin, do an ERwin report, and then compare the two report’s data.