Since our second rollout for live testing, the system has performed very well with only a few minor issues needing to be fixed. The system has performed better than expected, and I have been able to bring forward the next step in testing by two weeks.
The Next Step:
Initially the plan was to run the system in live testing for a full month with the two test card types previously migrated, then at the end of the month increase the migration of card types to 50%. However, with the success of the testing so far, I am confident I can move to the next step early.
The plan is to now migrate 50% of all card types (completed this evening), and continue to monitor and update the system as required for two months before taking the migration process to 100%.
In relation to the issue regarding storing images in the file system rather than the database, at 50% migration the database backup is only 75mb, which is well within the allowable storage limits enforced by the clients virtual server configuration. So when it comes time to migrate 100% of the card types storage will not be an issue.