Is this benchmark sufficient to consider my algorithm as an efficient matrix multiplication algorithm?
one thing I want to mention is that the strassen's matrix multiplication algorithm isn't often used in the real world and your algo is probably faster if the $n$ stays below a few thousands (explained here: https://stackoverflow.com/questions/13559928/why-is-my-strassens-matrix-multiplication-slow).
Now if you still want to compare your algorithm to the strassens algorithm I would recommend you to copy past a function from somewhere and run it on your computer.
The algorithm would get the same input as your algo and would run on the same hardware.
Here are some implementation of strassens algo:
vectors:
https://github.com/dmonaldo/strassen-matrix-multiplication/blob/master/main.cpp
arrays:
https://www.geeksforgeeks.org/strassens-matrix-multiplication-algorithm-implementation/
When I benchmark an algorithm I always want to plot the results to visualize the complexity. I think more is better; so you should probably use more n not only 256, 512, 1024. Also it would be good to know if your algo is made for a special case like sparse matrices etc. if that's the case you need to pay close attention to the input data, otherwise one algo might have a disadvantage.