The United States Air Force Museum has a research area. In 1991 and again in 1992 I visited this area, an appointment is necessary. They had data on a test of a KI-84 vs a P-51D Mustang done postwar. These included all the relevent comparison graphs and other associated test pilot notes/figures/data.
I do not think I have a copy of this anymore. As I cleaned up during a move of address, and was no longer playing flight sims.

I will check when I get home.
If you have never been to the museum go. If you are interested in data and photographs of WWII aircraft, goto the research area. Its a fascinating place with tons of file cabinets and that is just the tip of the iceberg of their collection which they will research into for a fee.
(All data in the above post was current as of 1992, access to and quality of the aforementioned research area may have changed, the poster is not responsible for any changes or errors in the processes mentioned above)