by condensing data, you basically combine prior years' transactions into one GL entry per month and lose all the details, (certain transactions are not condensed, such as payroll etc, I am not sure, please check to confirm). Therefore, it is advised that you back up prior year file, just in case you need to find out detailed transaction info. you can still restore that file and access such info, hopefully not that frequently. e.g. you can condense anything is three years old depending on your business. this way, your file could shrink by almost 50% in your case to 3/7). Another way to improve speed is to make unused account, items etc inactive, it also release some system capacity.

The key here is the keep backups documents and have them properly named for future reference.

Correct me if I am wrong. Thanks and good luck