Windows – More efficient file compression program for many identical files

I am doing a backup of my work and I'm looking for a program that can more efficiently compress files. The windows default compression program works fine, but it doesn't work as "smart" as i would like.

My files are basically entire snapshots of my work taken over the past few months as I do my regular complete backups. not a whole lot changes between the backups and many files are simply copies of each other.

My entire file set is approximately 15GB uncompressed, while individual snapshot backups (compressed using standard compression programs) are approximately 150 to 200 MB each (they typically increase in size with more recent dates). The total size of all the compressed snapshots is about 3GB. Due to the nature of the files, I expect a "smart" compression program to take the entire volume down to around 400-500 MB, that is, taking into account reasonable inefficiencies and extra space to compress the differences in the files.

Is there a compression program that will take advantage of the fact that many files are identical to achieve a much higher compression ratio than the standard windows compression program?

Thanks
-Faken

Edit: Just finished a best compression of the entire volume using standard windows compression. It is only 10MB better than the compressed snapshots combined. In my opinion that is unacceptable knowing the nature of the files.