you could do it using some of the custom fields and maybe a macro to overwrite the older data, so maybe you have numbers 1-10 for your delay and 11-20 for the %complete and always copy 9->10 and 8->9 etc so that you are keeping only the last 10 entries but to be honest I would do this in excel as you will be able to keep more data.
You can use a macro to output from MSP to excel.